An emerging trend in Novel Psychoactive Substances (NPSs): designer THC | Journal of Cannabis Research

Semi-synthetic pseudo-natural cannabinoids (SSPNCs)

Under this sub-group all Δ⁹-THC constitutional isomers can be found: the best-known naturally occurring isomer is Δ⁸-THC, in which the double bond is shifted to the adjacent position between C8 and C9. Other isomers are generated by the sequential shift of the double bond: Δ^6a,10a-THC, Δ^6a,7-THC, Δ¹⁰-THC, and Δ^9,11-THC (also known as exo-THC). Some of these compounds are degradants of Δ⁹-THC under particular conditions of pH, but their natural existence in the cannabis plant, albeit in traces, cannot be ruled out. Several isomers of Δ⁹-THC can be identified in a typical chromatogram obtained by high performance liquid chromatography couple to high-resolution mass spectrometry (HPLC-HRMS), some of which are likely to correspond to the compounds mentioned above. Certain websites promoting or describing these compounds claim that they occur naturally in trace amounts in the plant (Schmidt 2022). Δ⁷-THC was excluded in this isomers list as its recreational use has not been documented, most likely because of either the lower binding affinity for CB1R and activity in vivo or the laborious synthesis. Although THCA is a fully natural cannabinoid, thus should not be seen as a pseudo-natural compound, it was included in this section due to its close affinity. Other SSPNCs included are HHC, along with its carboxylated precursor hexahydrocannabinolic acid (HHCA) and one of its hydroxyl metabolites (10-hydroxy-HHC), and dihydrocannabinol (DHC), a Δ⁹-THC with an additional double bond on C6a-C10a.

Tetrahydrocannabinolic acid (THCA) diamonds

(6aR,10aR)-1-Hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromene-2-carboxylic acid.

“Diamonds” is an umbrella word used to refer to the crystal form of a pure compound derived from C. sativaL. Available online for purchase are “Cannabis Diamonds”, “CBD Diamonds” and “THCA Diamonds” (MediaBros 2022). For the scope of this review only THCA Diamonds will be discussed.

Chemistry and synthesis

THCA diamonds (also “THC Diamonds” or “THCA/THC Crystals” and, possibly, “Cannabis Diamonds”) are basically made of almost pure (purity higher than 99%) Δ⁹-THCA.

C. sativa L. produces two different acidic forms of Δ⁹-THCA: Δ⁹-THCA-A showing the carboxylic group in ortho position to the aromatic hydroxyl function and Δ⁹-THCA-B with the carboxylic group in para position to the aromatic hydroxyl group. The former is the main enzymatic product of THCA synthase and is predominant in the plant, while the latter is only produced in small amount. Despite their structural similarities they show a substantial difference in the decarboxylation attitude (the B form is extremely more stable) and in the stability of the crystalline form (Filer 2021; Mechoulam et al. 1969).

In the absence of an extensive characterization of THCA diamonds available on the market, it is reasonable, from the authors’ point of view, to deduce that they should be mainly made of Δ⁹-THCA-A, being Δ⁹-THCA-B less available and less exploitable for recreational use.

Indeed, according to descriptions available online, THCA diamonds are obtained when the raw material undergoes cold extraction, mainly employing butane, repeated purification steps and lastly a slow removal of the solvent leading to crystallization of the isolated cannabinoid. When the process is correctly run it yields a pure final product with no hint of terpenes and flavonoids, thus some manufacturers add a mixture of them (the so called “diamond sauce”) to restore some entourage effect. This kind of product is also commercially known as “diamonds in sauce”) (Delphi 2022).

This production technique raises legal concerns. Due to reasons related to yield, the extraction is likely made from marijuana rather than hemp. This means the process would involve an illegal and untraceable product, leading to doubts about the safety guarantee of the final product.

Alternative synthetic paths may involve CBD as a starting reagent. At present, this is only discussed in specialized online forums, but it could become a feasible solution due to the absence of legal issues and the greater availability of CBD.

Apart from those risks posed by the high concentration of active substance, the main health issues arising from the consumption of diamonds are therefore due to the possible presence in the final product of solvents residues from the extraction and purification steps (Burb n.d.).

Pharmacology

Δ⁹-THCA is largely known for being the non-psychoactive cannabinoid originally produced by C. sativa L., then turned into its psychoactive counterpart through heat-induced decarboxylation. This is why recreational use of this plant has traditionally been based on smoking, today accompanied by other practices like dabbing, vaping, etc. Similarly, the preparation of Δ⁹-THC edibles always involves a cooking/baking step.

The non-psychoactive nature of Δ⁹-THCA has always been explained by the lack of binding affinity at the human CB1R, even if data in the scientific literature were not in accordance reporting an affinity sometimes equal to THC or 25-fold weaker or totally absent (McPartland et al. 2017). In their 2017 study on THCA’s affinity and efficacy at the human cannabinoid receptors h CB1R and hCB2R, McPartland et al. highlighted the importance of materials purity that had to be checked prior any test (McPartland et al. 2017). Indeed, THCA is particularly susceptible to losing the carboxylic group even when stored at freezer temperatures and they suggested that when hCB1R activity is found this is due to the presence of THC impurities rather than to THCA itself (McPartland et al. 2017).

A. Zagzoog et al. explored THCA’s biological activity in vitro and in vivo. In vitro tests evaluated its activity on each hCBR in Chinese hamster ovary (CHO) cell membranes through the displacement test using [³H]CP55,940 as reference material. Unlike Δ⁹-THC (K_i = 36 nm), the competition displacement assays indicated that THCA could not fully displace [³H]CP55,940 from hCB1R (K_i = 620 nM), but showed a small but significant displacement from hCB2R (K_i= 1.3 nM), most likely indicative of a non-competitive binding (Zagzoog et al. 2020). In vivo evaluation was performed through the tetrad assays on any cataleptic, hypothermic, anti-nociceptive, locomotive, and anxiety-modifying activity. The study attributed to ∆⁹-THCA anti-nociceptive and hypolocomotive effects at 3 and 10 mg/kg and anxiolytic-like effects at 10 mg/kg (Zagzoog et al. 2020).

Identification and analysis

In recent years, several analytical techniques for the analysis of products derived from C. sativa L. have increasingly been tested as a consequence of the in-depth investigations on the pharmacological effects of the various compounds produced by the plant but also because its use is becoming progressively legal and accepted.

The two most common analytical methods are based on gas (GC) and liquid (LC) chromatography. In GC high temperatures in the injection port and in the oven turn Δ⁹-THCA into Δ⁹-THC, thus in the analytical result the specific contribution of each of them remains unknown. The only way to separately determine the two compounds is a derivatization step during sample preparation prior to GC analysis, which is not needed in the HPLC technique. In GC, chromatographic separation is often obtained through a low polarity stationary phase, as for instance made of 5% diphenyl- and 95% dimethyl polysiloxane, and specificity may be further increased with tandem GC (GC×GC). The chromatographic dimension may be coupled with a Flame Ionization Detector (FID) or a mass spectrometer (MS).

The rationale of the GC approach without derivatization, as mentioned above, is based on the conversion of Δ⁹-THCA into Δ⁹-THC. This represents a sensitive matter when the analysis is run for legal or forensic purposes. As this technique combines the undefined contributions of the carboxylated and decarboxylated compounds, the final analytical outcome loses its qualitative significance. Moreover, the presence of the illegal Δ⁹-THC in the analytical results does not necessarily imply that it was already present in the original sample, at least in the amount indicated by the numerical data, but rather derived from the conversion of the carboxylated precursor Δ⁹-THCA.

High performance liquid chromatography (HPLC) is the most suitable technique for the analysis of THCA. Being run at ambient temperature, it prevents its decarboxylation and allows for a separate identification and quantification of neutral Δ⁹-THC and acidic Δ⁹-THCA. The best separation between chromatographic peaks is obtained through a C₁₈ stationary phase. The liquid chromatographer may be conventional or an ultra-high performance one with better separations at higher speed thanks to columns packed with stationary phases with particles smaller than 2 μm. It may be coupled to detectors, usually mass spectrometry (MS) or a UV/DAD (Diode Array Detector). The DAD is able to provide more details on the chromatographic peak improving method specificity as Δ⁹-THCA has an absorption spectrum that differs from that of its decarboxylated form. On the other hand, MS offers the greatest potential thanks to high-resolution detectors (HRMS such as QToF and Orbitrap) responsible of a higher specificity in case of extracts from complex matrices compared to UV/DAD. Moreover, HRMS enables the distinction between different compounds with the same nominal mass (isomers).

In light of the above, HPLC/UHPLC coupled to HRMS currently stands as the most powerful and versatile technique for the analysis of complex mixtures of cannabinoids. In particular, this approach allows for the determination of the exact mass of each compound, the independent quantification of both carboxylated and decarboxylated form of several cannabinoids (including THCA) without the need of derivatization. Consequently, it provides a more comprehensive characterization of each sample.

Several examples are present in the literature regarding the analysis of THCA in several matrices, including commercial products and biological specimens, employing both the GC-MS technique with derivatization (Nahar et al. 2020) and the HPLC-HRMS technique (Nahar et al. 2020). With specific focus on the analysis of THCA diamonds, it is not possible to find any scientific work, but some companies selling the product also provide the certificate of analysis. The most common routine technique employed in this case is HPLC coupled to either DAD or UV detector (SCLabs 2022; Analytical GP 2021; Inc. SAS 2023).

Recreational use

THCA diamonds are described as a very appealing substance intriguing the user both for its form and colour but above all because they are known as a concentrated legal form of THC (TheChronicBeaver 2021).

Online sites and personal blogs dealing with THCA diamonds explain their composition, production, the origin of the colour and warn about the possible presence of solvent residues. They advise how to use them as they need to undergo a decarboxylation process, thus eating them in the raw form does not produce an effect (Delphi 2022). Moreover, most people suggest that the best way to get the most of them is vaping or dabbing and recommend to consume them in progressively increasing doses (TheChronicBeaver 2021; Bortolazzo n.d.).

On the online forums, some people do not seem enthusiastic about THCA diamonds effects with respect to traditional cannabis products and suggest to blend them with terpenes or cannabis for a better experience confirming, from their perspective, the so called “entourage effect” (reddit.com. 2021). Others add more details and state that “white” diamonds produce a more “head” experience while diamonds “in sauce” produce a more “bodily” high and are more similar to the original cannabis plant material (Bluelight n.d.).

Δ⁸-Tetrahydrocannabinol (Δ⁸-THC)

(6aR,10aR)-6,6,9-Trimethyl-3-pentyl-6a,7,10,10a-tetrahydrobenzo[c]chromen-1-ol.

Chemistry and synthesis

Δ⁸-THC derives from an acid- or oxidatively promoted shift of the endocyclic double bond to the more thermodynamically stable position Δ⁸ (Razdan 1981). It is known since 1942 when it was synthesized by electrophilic cyclization of CBD and used in human studies (Adams 1942). Because of the Agricultural Improvement Act (Farm Bill Act), which include “all derivatives, extracts, cannabinoids, isomers, acids, salts and salts of isomers” in the definition of “hemp” (Agriculture Improvement Act of 2018 2018), Δ⁸-THC has been erroneously considered a legal product when it is derived from hemp CBD. The conversion reaction of CBD into Δ⁹-THC is known since the early 1960s thanks to Gaoni and Mechoulam’s studies (Gaoni and Mechoulam 1964) and a couple of years later they observed that either strong or mild acidic conditions in the reaction lead to different products (Gaoni and Mechoulam 1966). In particular, Δ⁹-THC is obtained from CBD upon treatment with HCl (0.0.5% in absolute ethanol) for 2 h, while Δ⁸-THC is obtained in relatively high yield by treating CBD with p-toluensulfonic acid (pTSA) for 18 h (Gaoni and Mechoulam 1966). Over the years the synthetic procedure for the manufacturing of Δ⁸-THC has not changed and the products circulating on the market are prepared according to the original procedure (Gaoni and Mechoulam 1966).

The major concern about the illicit manufacturing of Δ⁸-THC products is the presence of a number of contaminants, some of which are also toxic. Besides the presence of Δ⁹-THC in concentrations exceeding the legal limit, other contaminants can include Δ⁷-THC, Δ¹⁰-THC, Δ¹¹-THC, 11-OH-CBD, 11-OH-THC, 5’-OH-CBD, 11,5’-diOH-CBD, 11,5’-diOH-THC, Δ⁸-iso-THC, Δ⁴⁽⁸⁾-iso-THC, and various substituted hexahydrocannabinols (HHCs), such as 9α-OH-HHC and 8-OH-iso-HHC (Kiselak et al. 2020), heavy metals in quantities non-compliant with the USP (copper, chromium and nickel), solvents (dichloromethane, methanol, ethyl acetate, and isopropanol) and several unknown cannabinoids (USCC 2021).

Pharmacology

Since its discovery, Δ⁸-THC was used in animal and human studies and found to exert a cannabimimetic activity similar to that of its isomer Δ⁹-THC (Adams 1942). The results of the in vitro activity are quite different among the experiments across the years, but it can be concluded that Δ⁸-THC has a slightly lower CB1R binding affinity compared to its regioisomer Δ⁹-THC (K_i = 41 ± 1.7 nM for Δ⁹-THC vs. K_i = 45 ± 12 nM for Δ⁸-THC (Martin et al. 1999)). Also, a different balance of CB1R vs. CB2R activation and a different formation rate of the active 11-OH metabolite contribute to a lower in vivo potency of Δ⁸-THC compared to Δ⁹-THC. However, further studies are required to clarify this difference, especially CB1R and CB2R binding affinity experiments in human and rodent under equivalent experimental conditions, which is important for assessing translatability of in vivo studies to humans (Tagen and Klumpers 2022).

Identification and analysis

Synthetic (-)-trans-Δ⁸-THC was characterized by proton and carbon nuclear magnetic resonance (¹H NMR and ¹³C NMR) spectroscopy (Huang et al. 2010; Choi et al. 2004; Archer et al. 1977), hetero NMR (Bluelight n.d.) spectroscopy, infrared (IR) spectroscopy (Huang et al. 2010), UV-Vis (Hazekamp et al. 2005; De Backer et al. 2009) spectroscopy and mass spectrometry (MS) (Huang et al. 2010; Hazekamp et al. 2005).

In analytical investigations Δ⁸-THC behaves in a very similar way as Δ⁹-THC. Therefore, it is important to distinguish between Δ⁹-THC, Δ⁸-THC and all the other isomers. A great number of papers have been published on this topic and cover the analysis of Δ⁹-THC and Δ⁸-THC and in some cases other THC isomers in a wide range of matrices, including plant material, CBD oil, e-cigarette liquids, foods and beverages, but also biological specimens (blood, urine, oral fluid) (Tagen and Klumpers 2022).

For non-biological fluids, the most common analytical technique for the analysis of THC isomers, including Δ⁸-THC, is HPLC-UV (or HPLC-DAD) under reverse-phase conditions. Such methodology ensures good resolution between Δ⁹-THC and Δ⁸-THC (Citti et al. 2020; Micalizzi et al. 2021; Song et al. 2022). However, as THC isomers show very similar spectroscopic properties, such detection techniques lack specificity and are not able to separate very complex mixtures. HPLC-HRMS, besides the higher sensitivity compared to HPLC-UV, provides differentiation between the several isomers through the different mass fragmentation patterns and identification of synthetic side products (Kiselak et al. 2020; Pellati et al. 2018). Similarly, GC-MS is also able to distinguish between several THC isomers (Sams 2022).

In biological fluids Δ⁸-THC is generally detected and quantified as a chemical entity different from Δ⁹-THC by HPLC-MS/MS (Reber et al. 2022). For example, the method developed by Reber et al. also included the separation of exo-THC (Δ^9,11-THC), ∆^6a,10a-THC and ∆¹⁰-THC to exclude potential interfering compounds (Reber et al. 2022).

A comprehensive review on the chromatographic resolution of Δ⁹-THC isomers in different matrices has been recently published by La Maida et al. (2022).

Recreational use

According to informative websites, Δ⁸-THC produces a mild psychoactive experience that users describe as calming and euphoric. It can reduce feelings of nausea and provides many other effects like relaxation, euphoria and relief from pain. Most consumers have reported a noticeably milder experience compared to Δ⁹-THC together with sedative effects (Schmidt 2023). As a result, the side effects like paranoia are remarkably milder.

Nowadays, it is possible to find Δ⁸-THC in many cannabis and hemp-based products including distillate cartridges and syringes, vape cartridges, tinctures, oils, concentrates, gummies and edibles, beverages, and flowers (sprayed with Δ⁸-THC) (Schmidt 2023).

Δ¹⁰-Tetrahydrocannabinol (Δ¹⁰-THC)

(6aR,9R)-6,6,6a,9-Tetramethyl-3-pentyl-6a,7,8,9-tetrahydro-6H-benzo[c]chromen-1-ol and (6aR,9S)-6,6,6a,9-tetramethyl-3-pentyl-6a,7,8,9-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

This isomer of Δ⁹-THC was originally synthesized by Srebnik et al. in 1984. As two epimers are possible, each one can be obtained with significant excess following two procedures starting from Δ⁹-THC: procedure A involves the use of t-pentyl potassium in toluene-hexamethylphosphoric triamide (HMPA) (6: 1) at reflux temperature, while procedure B requires the use of n-butyl-lithium in hexane (1.65 M) and HMPA at 0 °C (Srebnik et al. 1984). Basically, it is possible to start from CBD, which is converted into Δ⁹-THC and follow either one procedure or the other. Under the conditions of procedure B, an 8:1 mixture of (6aR,9S)-Δ¹⁰-THC and (6aR,9R)-Δ¹⁰-THC; on the other hand, procedure A leads to a 1:9 mixture of (6aR,9S)-Δ¹⁰-THC and (6aR,9R)-Δ¹⁰-THC respectively (Srebnik et al. 1984).

Pharmacology

Early studies on pigeons trained to discriminate between the presence and absence of Δ⁹-THC demonstrated that the (6aR,9R) epimer of Δ¹⁰-THC was the active compound in terms of cannabimimetic effects, while the (6aR,9S) epimer was inactive (Järbe et al. 1988). It is also reported that even the active epimer (9R) is less active that the active epimer of Δ^6a,10a-THC (9S) (see next paragraph), which in turn is less active than Δ⁹-THC (Järbe et al. 1988). No data is available on the CB1R and CB2R affinity of the two epimers of Δ¹⁰-THC, thus no comparison with Δ⁹-THC can be made in terms of in vitro binding affinity.

Identification and analysis

Synthesis and full characterization of pure epimers (9R)-Δ¹⁰-THC and (9S)-Δ¹⁰-THC was performed by Srebnik et al. reporting optical rotations, UV, IR, NMR and MS spectra (Srebnik et al. 1984). The two epimers of Δ¹⁰-THC, along with those of Δ^6a,10a-THC, were resolved at the baseline using an HPLC-UV method in normal phase (NP) conditions (95:5 hexane:isopropanol) (Williams et al. 2021). Moreover, the same isomers were successfully resolved using chiral stationary phases (CSPs) as recently reported by Umstead (2021). In details, the author used the CHIRALPAK IG-³ and the CHIRALPAK IB N-₃CSP in NP conditions eluting either 95:5 hexane-ethanol or 90:10 hexane-isopropanol, though the two CSPs gave inverted elution orders (Umstead 2021).

Other methods include GC-MS applied to vaping liquids to distinguish between Δ⁹-THC, Δ⁸-THC, Δ^6a,10a-THC, (9R)-Δ¹⁰-THC, (9S)-Δ¹⁰-THC, Δ^9,11-THC, cannabinol (CBN), CBD, and olivetol (Ciolino et al. 2021), and lastly a bidimensional LC-MS/MS applied to e-cigarette cartridges, where the authors identified Δ⁹-THC, Δ⁸-THC, Δ^6a,10a-THC, Δ¹⁰-THC, and CBD (Chan-Hosokawa et al. 2021).

Recreational use

Cannabinoids users describe Δ¹⁰-THC as an uplifting and energizing substance with a gentle head buzz (Schmidt 2023). Many users report that it enhances motivation, creativity, and cognitive function (Schmidt 2023). Reddit users claim similar effects to Δ⁸-THC, albeit less potent, that lead more to a “mind high” rather than a physical body high (reddit.com. 2020). Δ¹⁰-THC based products are increasingly spreading worldwide in the form of disposable pens, vape cartridges, gummies, tinctures and oils, dabbing syringes, chocolate bars, lollipops, shatter, flowers, and pre-rolls (sprayed with Delta-10 distillate) (Schmidt 2023).

Δ^6a,10a-Tetrahydrocannabinol (Δ^6a,10a-THC)

(S)-6,6,9-Trimethyl-3-pentyl-7,8,9,10-tetrahydro-6H-benzo[c]chromen-1-ol and (R)-6,6,9-trimethyl-3-pentyl-7,8,9,10-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

This isomer was first synthesised by Adams and Baker in (1940). Condensation of ethyl 5-methylcyclohexanone-2-carboxylate with olivetol, followed by addition of methylmagnesium iodide, afforded the product as a colourless viscous oil in 78% yield (Adams and Baker 1940). In 2014 Rosati et al. published a one-pot heterogeneous synthesis of Δ^6a,10a-THC (or Δ³-THC according to the old numbering) starting from an equimolar mixture of either (R)-(+)-pulegone or (S)-(−)-pulegone and olivetol in 1,2-dichloroethane (Rosati et al. 2014). The reaction was carried out in the microwave using either α-zyrconium sulphenylphosphonate [(α-Zr(O₃PCH₃)_1.2(O₃PC6H₄SO₃H)_0.8], sulfuric acid supported on silica gel [H₂SO₄–SiO₂], ytterbium triflate [Yb(OTf)₃], or ytterbium triflate-ascorbic acid [YTACA 1:10] as catalyst (Rosati et al. 2014). Both epimers could be obtained with 49% and 47% yield for (9R)- and (9S)-Δ^6a,10a-THC, respectively, and a purity of 98% for both compounds (Rosati et al. 2014).

Pharmacology

The dog ataxia test revealed that the two epimers and the racemic mixture behaves differently with the laevorotatory epimer being four to five times more active, and the dextrorotatory epimer two to three times less active than the racemate, although no comparison was made with Δ⁹-THC (Adams et al. 1942). Later, Hollister et al. tested the epimers and the racemate in humans, observing that the (9S) epimer was the active one producing one third to one sixth the effects of Δ⁹-THC (Hollister et al. 1987). On the other hand, the (9R) epimer did not bring any psychoactive effects as the activity did not change when the two epimers were administered together in a 1:1 mixture (Hollister et al. 1987). In 2014, Rosati et al. measured the CB1R and CB2R binding affinity of both epimers, revealing that CB1R affinity of (9S)-Δ^6a,10a-THC was higher (K_i = 5 nm) than that of Δ⁹-THC (K_i = 22 nm), while the one of the (9R) epimer was in the range of that of Δ⁹-THC (K_i = 29 nm). Both epimers showed similar affinity for CB2R (K_i = 17 and 18 nm for (9S)- and (9R) epimer, respectively), which was higher than that of Δ⁹-THC (K_i= 46 nm) (Rosati et al. 2014).

Identification and analysis

Identification of pure enantiomers (R)-(+)-Δ^6a,10a-THC and (S)-(−)-Δ^6a,10a-THC was described by Srebnik et al. reporting optical rotations, UV, IR, NMR and MS spectra (Srebnik et al. 1984).

The few analytical methods for the analysis of Δ^6a,10a-THC reported in the literature match those described above for Δ¹⁰-THC (Williams et al. 2021; Umstead 2021; Ciolino et al. 2021; Chan-Hosokawa et al. 2021).

Recreational use

On informative websites, it is reported that Δ^6a,10a-THC has the same effects as Δ¹⁰-THC, thus milder than Δ⁹-THC (Schmidt 2022). Some people report uplifting and energizing effects (similar to Δ¹⁰-THC); many users also report a heightened sense of mental clarity and focus without paranoia and anxiety (Schmidt 2022).

As this compound is quite new on the recreational market, it is sometimes mislabelled as Δ¹⁰-THC (and vice versa).

10-Oxo-Δ^6a,10a-Tetrahydrocannabinol (10-Oxo-Δ^6a,10a-THC)

(R)-1-Hydroxy-6,6,9-trimethyl-3-pentyl-8,9-dihydro-6H-benzo[c]chromen-10(7H)-one and (S)-1-hydroxy-6,6,9-trimethyl-3-pentyl-8,9-dihydro-6H-benzo[c]chromen-10(7H)-one.

Chemistry and synthesis

In 1975, Friedrich-Fiechtl and Spiteller isolated 10-oxo-Δ^6a,10a-THC from a hashish extract by preparative thin layer chromatography (TLC) (Friedrich-Fiechtl and Spiteller 1975). Two years later, Kettenes-van den Bosch and Salemink discovered this compound in cigarette smoke condensate, specifically in the neutral fraction (Kettenes-van den Bosch and Salemink 1977). Lewis et al. identified the compound in decarboxylated medicinal cannabis extracts and highlighted its absence in the native extracts, suggesting that the product is released upon heating (Lewis et al. 2017). No record is present in the literature regarding the synthesis of 10-oxo-Δ^6a,10a-THC, but it rather seems it can be isolated from cannabis extracts following decarboxylation. It is likely a decomposition product of Δ⁹-THC, although information on the enantiomeric composition of the spontaneously formed product is currently unavailable.

Pharmacology

No research has been conducted on the pharmacology of this cannabinoid but it is believed to act as Δ⁹-THC on CB1R.

Identification and analysis

The pure compound has been characterized by GC-MS, NMR, FT-IR (Friedrich-Fiechtl and Spiteller 1975; Kettenes-van den Bosch and Salemink 1977), and HPLC-MS in RP conditions (Lewis et al. 2017). Its quantification has been achieved by GC-FID in cannabis smoke condensate after separation of three fractions: acidic, phenolic and neutral, the latter being the one containing this specific compound (Friedrich-Fiechtl and Spiteller 1975; Kettenes-van den Bosch and Salemink 1977).

Recreational use

10-Oxo-Δ^6a,10a-THC is not widespread for recreational use, but some websites promote the compound supposing it has similar properties as Δ⁹-THC (Hewett 2022; What is 10-Oxo-Δ6a(10a)-tetrahydrocannabinol (OTHC)? 2023).

Δ^9,11-Tetrahydrocannabinol (Δ^9,11-THC)

(6aR,10aR)-6a,7,8,9,10,10a-Hexahydro-6,6-dimethyl-9-methylene-3-pentyl-6H-dibenzo[b,d]pyran-1-ol.

Chemistry and synthesis

Δ^9,11-THC is known since the late 1960s, when it was first synthesized by Fahrenholtz et al. from olivetol and diethyl α-acetoglutarate leading to the racemic mixture of the compound (Fahrenholtz et al. 1967). This type of synthesis would make it a completely synthetic Δ⁹-THC derivative, but another synthetic procedure was developed by Wildes et al. from either Δ⁸-THC or Δ⁹-THC with potassium tricyclopentylcarbinolate to obtain the pure stereoisomeric forms in 40–45% yield (Pitt et al. 1971). Further improvements were made in the late 1980s using Δ⁸-THC as the precursor for the synthesis, which is converted into a 3:1 separable mixture of (9R)-chlorohexahydrocannabinol ((9R)-Cl-HHC) and (9S)-Cl-HHC by adding gaseous hydrochloric acid and zinc chloride (Banijamali and Makriyannis 1988). The product was obtained in 65% overall yield by HCl elimination with potassium t-amilate (Banijamali and Makriyannis 1988). Either Δ⁸-THC or Δ⁹-THC can be used as precursors as they both are converted into a mixture of (9R)-Cl-HHC and (9S)-Cl-HHC with excess of the former (Banijamali et al. 1998).

There is no record on the natural occurrence of such cannabinoid, although it is reported also as a very small impurity of Δ⁹-THC isomerization after decarboxylation of the plant material (Cid and Van Houten 2015). Nonetheless, it would still represent a minor component whose extraction would not be cost-effective. In light of the above, the synthesis of Δ^9,11-THC, specifically the semi-synthesis, is the most feasible way starting from the legal CBD.

Pharmacology

Δ^9,11-THC is not as psychoactive as Δ⁹-THC. Indeed, its cannabimimetic activity was found to be one twentieth of the parent compound when tested on rats for their activity in the cage (Christensen et al. 1971) and one fifteenth in a multiple test (locomotor activity, tail-flick latency, hypothermia, ring immobility) on rats (Compton et al. 1991). These results are in line with its CBR (supposedly CB1R) binding affinity (K_i [Δ^9,11-THC] = 334 nm, vs. K_i [Δ⁹-THC] = 218 nM) (Compton et al. 1991). However, it is interesting to note that Δ^9,11-THC is only 4-fold less potent than Δ⁹-THC in the generation of the antinociceptive response in the mouse (Compton et al. 1991).

In another study, Δ^9,11-THC resulted 100-fold less potent than Δ⁹-THC in producing hypothermia, analgesia, lethality and in reducing spontaneous activity in mice, while it did not show any cannabimimetic effects in dogs (static ataxia, hyperreflexia, prancing and tail-tuck) and rhesus monkeys (ptosis, sedation and ataxia) (Beardsley et al. 1987).

Besides the lower affinity for CB1R, the lower potency of Δ^9,11-THC compared to Δ⁹-THC can be also justified by the failure to produce the well-known metabolite 11-hydroxy-THC, which has even stronger effects than the parent compound Δ⁹-THC.

Identification and analysis

Besides the full characterization of the pure compound by NMR, FT-IR, and MS (Fahrenholtz et al. 1967), Δ^9,11-THC was analyzed in mixture with Δ⁹-THC and Δ⁸-THC by HPLC-UV in NP conditions by Banijamali and Makriyannis (1987), in mixture with other cannabinoids by HPLC-UV in RP conditions (Krepich et al. 2020; Franklin and Wilcox 2019), and in vaping liquids by HPLC-DAD in RP conditions (Ciolino et al. 2021).

Recreational use

Δ^9,11-THC can be found in several products like vaping liquids, cartridges, sauces and waxes with various names including delta-11-THC and exo-THC in combination with other cannabinoids (Ciolino et al. 2021; reddit.com 2021). However, the name delta-11-THC is also used improperly to indicate 11-hydroxy-THC, which is the primary Δ⁹-THC metabolite. Exo-THC is advertised as an exotic component in hemp derived products (reddit.com 2021).

There are not many reports on the recreational experience of exo-THC, highlighting the quite recent attention to this cannabinoid, but a user on reddit.com declared that consuming a “full spectrum” vape cartridge labelled with CBD, cannabichromene (CBC), cannabigerol (CBG), CBN and other minor cannabinoids including exo-THC (8.27%), cannabitriol (CBT) (10.5%), and cannabielsoin (CBE) (5.72%) led to a “good spacey feeling” and slow reaction time, though keeping a clear head sensation (reddit.com. 2023). However, given the complexity of the cannabinoid mixture in the product, the effects might be ascribed to some other compound.

11-Hydroxy-tetrahydrocannabinol (11-OH-THC)

(6aR,10aR)-9-(Hydroxymethyl)-6,6-dimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

11-Hydroxy-Δ⁹-THC (11-OH-THC) is the primary metabolite of Δ⁹-THC formed in the liver by the enzymatic activity of the CYP450 family (in particular CYP2C9 and CYP3A4) (Huestis 2005). Both oral consumption and inhalation of either the parent compound Δ⁹-THC or THC-containing products lead to the formation of this metabolite.

The chemical synthesis of the pure compound is neither facile nor high-yielding (Pitt et al. 1975), even starting from the legal CBD (Kiselak et al. 2020). Therefore, the only efficient way of making 11-OH-THC is using either rat microsomes (Wall et al. 1970) or liver homogenates (Wall 1971;  Nilsson et al. 1970), which lead to a 30% yield for the product.

Pharmacology

11-OH-THC is known to exert a several fold higher potency compared to the parent compound Δ⁹-THC both in vitro (with a K_i of 0.37 nm vs. 35 nm of Δ⁹-THC) (Zagzoog et al. 2022) and in vivo (Lemberger et al 1972, 1973). In a double-blind randomized experiment on humans, the 11-OH metabolite was reported to produce a greater psychoactive high in all subjects compared to Δ⁹-THC (Lemberger et al. 1973). In the same work, the intravenous administration of 11-OH-THC led to pronounced psychologic and pharmacologic effects within 2–3 min (marked tachycardia, intense psychologic high, etc.) (Lemberger et al. 1973). On the other hand, the intravenous administration of Δ⁹-THC had qualitatively similar effects, though not reaching their peak until 15–30 min (Lemberger et al. 1973). This and other studies, such as that of Lemberger et al. (1972), strongly support the hypothesis that the psychoactivity of Δ⁹-THC comes from its active metabolite since the effects of the latter show a good temporal correlation with the plasma levels of its metabolite.

Identification and analysis

Numerous validated methods are reported in the literature for the determination of 11-OH-THC in several matrices, usually in combination with Δ⁹-THC and other metabolites like Δ⁹-THC carboxylic acid (11-THC-COOH) and sometimes the glucuronic derivative by either GC-MS (Andrenyak et al. 2017; , Purschke et al. 2016) or LC-MS/MS (Reinstadler et al. 2023; Simões et al. 2011). Notwithstanding their very high sensitivity, all methods have been developed for the determination of THC metabolites in biological specimens, such as urine (Morisue Sartore et al. 2022), blood (Lo Faro et al. 2022), serum (Pichini et al. 2021), plasma (Manca et al. 2022), hair (Lo Faro et al. 2022) and oral fluid (Gorziza et al. 2023), not for the detection of such compounds in commercial products. Nonetheless, KCA Laboratories have tested a product claiming to contain 11-OH-Δ⁸-THC for purity, though not specifying the methodology employed, and the manufacturer published the certificate of analysis (KCALabs 2023). However, no other analytical method has been published for the application to matrices different from the biological specimens.

Recreational use

Until a few months ago, 11-OH-THC based products seemed not to be actually sold on the market, but only advertised to attract the attention of consumers with “exotic” and “alternative” cannabinoids. Indeed, all products advertising the alleged cannabinoid 11-OH-THC have actually turned out to be fakes after chemical analysis. In October 2023, the first product containing over 96% 11-OH-Δ⁸-THC as distillate manufactured by 3CHI reached the recreational market (KCALabs 2023; 3CHI 1959). Although most consumers are aware the products they buy claiming high concentration of 11-OH-THC do not actually contain this cannabinoid, some of them reported quick onset of the effects and a strength somehow close to THC, along with the negative effects like an accelerated heartbeat and racing thoughts (reddit.com. 2023). However, due to the presence of other cannabinoids in the products it is difficult to ascribe such effects solely to the alleged 11-OH-THC.

Hexahydrocannabinol (HHC)

(6aR,9R,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydrobenzo[c]chromen-1-ol and (6aR,9S,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydrobenzo[c]chromen-1-ol.

Research groups have always been interested in the potentialities of hexahydrocannabinol (HHC) and its saturated analogues but today it has gained an important role also in the market for recreational substances (EMCDDA technical expert meeting on hexahydrocannabinol (HHC) and related cannabinoids [press release] 2022). Indeed, the oversupply of CBD enriched extracts and its use as a chemical precursor for several SSCs have led manufacturers to offer to the market a new series of cannabinoids exploiting synthetic routes known in the scientific literature for decades. Among this series of cannabinoids, HHC may be seen as an exotic compound in the cannabis consumer market but it is not exactly a new cannabinoid as it was discovered in 1940 by Adams and Todd in their laboratories while exploring with the hydrogenation reaction on the THC molecule in marijuana (Adams et al. 1940). Therefore, during the last two years, HHC has been openly sold on the internet websites as a “legal” and cheaper alternative to THC and cannabis (Graziano et al. 2023).

Chemistry and synthesis

HHC has three stereogenic carbon atoms, and all eight stereoisomers have been discussed in the chemical literature. Of these, only the semi-synthetic (6aR,9S,10aR)-HHC (9α-HHC) and (6aR,9R,10aR)-HHC (9β-HHC) epimers have attracted attention, and only these isomers appear to have been encountered in marketed products.

The first total stereoselective synthesis of natural (9R)-HHC and its unnatural (9S)-HHC diastereomer was developed by Tietze starting with 5-pentylcyclohexane-1,3-dione and optically pure citronellal via an intramolecular Diels-Alder reaction and aldol condensation followed by aromatization and elimination along a two-step reaction (Tietze et al. 1982). However, already in 1940 Adams performed the semi-synthesis of HHC by hydrogenation of Δ^6a,7-THC (Adams et al. 1940).

The semi-synthesis has been revised with several catalysts obtaining different yields and epimeric ratios (Gaoni and Mechoulam 1966; Cornia et al. 1989; Collins et al. 2023; Nasrallah and Garg 2023). In particular, the Garg’s group employed tri(acetylacetonato)iron(III) as the hydrogen atom donor catalyst for the radical reduction reactions in combination with thiophenol and sylilbenzene to reduce Δ⁸-THC (Nasrallah and Garg 2023). Under these conditions, the mixture of diastereomers afforded 77% of yield and an epimeric ratio of 11:1 ((9R)-HHC:(9S)-HHC).

Pharmacology

Since its discovery, HHC has been extensively studied both in vitro and in vivo for its pharmacologic and/or psychoactive effects although part of these studies, especially the oldest ones, are affected by the uncertain composition of the sample, thus their results are of difficult interpretation.

In vitro biological studies of HHC (both racemic mixtures and single epimers) dealt with its interaction with several different receptors and biochemical mechanisms such as cannabinoid receptors, opioid receptors, RPA1 ion channel activation, acetylcholinesterase inhibition, cytotoxicity to human lung fibroblasts and anticancer properties in four pancreatic cancer cells. Interestingly the 9β epimer generally shows a higher activity with respect to its 9α counterpart (Ujváry 2023).

In vivo tests (rabbit corneal reflex, tetrad test on mice, rhesus monkey behaviour, etc.) have been performed to assess cannabimimetic activity in comparison to Δ⁹-THC. Tests on rhesus monkeys, in particular, demonstrated that the cannabimimetic activity resided mainly, if not solely, in the laevorotatory 9β-HHC, with effects like ataxia, stupor, full ptosis, immobility, long lasting crouched posture, and absence of reaction (Edery et al. 1972; Mechoulam et al. 1980). Recent preliminary studies based on mouse tetrad assay confirmed the predominant cannabimimetic activity of the 9β epimer of HHC (Russo et al. 2023).

An important issue that HHC shares with all other commercialised semi-synthetic products is the possible contamination due to the synthetic pathway. Indeed, traces of heavy metals from hydrogenation along with byproducts of the other synthetic steps can be found in the final product because of the variable manufacturer’s expertise, differences in purification procedures and the absence of quality control (Ujváry 2023). Even the presence of an “analytical certificate” should not be considered a guarantee of product quality; indeed, the phenomenon of mislabelled products is currently widespread. For example, a GC-MS analysis revealed that a product sold as “HHC” in the United States was actually a mixture of Δ⁸-THC, Δ⁹-THC, Δ^6a,10a-THC, and CBN (Sams 2022).

Identification and analysis

Being one of the first investigated phytocannabinoid derivatives, HHC’s behaviour in the application of the most common analytical techniques seems, at present, well understood.

A precise separation of the two 9α/9β HHC epimers may be easily obtained by chromatography (TLC, GC and HPLC). Since the early studies, the relationship between the chemical structure and GC retention time of several common cannabis constituents and synthetic cannabinoids, (including HHC, hexahydrocannabivarinol (HHCV), and other linear and branched HHC homologs) were investigated with either unmodified or trimethylsilyl (TMS)-derivatized analyte (Vree et al. 1972, 1973). HPLC demonstrated the same versatility as GC in separating both phyto- and synthetic cannabinoids and the two HHC epimers as well (Stothard et al. 2023).

The detector of choice for structure identification is mass spectrometry. Fragmentation patterns in the mass spectra of the 9α and 9β epimers of HHC are virtually identical; hence, in the analysis of real samples the stereochemical composition may be achieved only by GC/HPLC-MS analysis followed by a confirmation run of a standard of known epimeric purity. In this regard, a very recent work by Kobidze et al. describes the development of the first LC-MS/MS stereoselective bioanalytical method using a CSP to quantitatively detect (9R)-HHC and (9S)-HHC and their metabolites in human blood, oral fluid and urine (Kobidze et al. 2024).

Another long-tested technique is UV-visible spectroscopy which gives spectrum of HHC with main absorption bands at λ_max272 and 282 nm in the UV region (Ujváry 2023).

¹H NMR spectroscopy is also useful to discriminate between the two epimers (Ujváry 2023). Solvent effects have been associated to the chemical shift of the C10 and C10a protons adjacent to the phenolic moiety.¹³C NMR spectra distinguish between the 9α and 9β stereoisomers since the carbon atoms of the cycloalkane fragment appear at different chemical shifts for the two epimers. Except for C6a, the chemical shift of all carbon atoms of the cycloalkane moiety of the 9β epimer is shifted downfield.

Finally, several different radioimmunoassay (RIA) methods have been developed over the years and primarily for the detection of Δ⁹-THC, but they all show a certain degree of cross-reactivity with other cannabinoids and their metabolites, including HHC, even if the latter is of unstated epimeric purity (Ujváry 2023). For this reason, it seems unlikely that an HHC specific immunoassay technique may be available in the future.

Recreational use

During the last two years, HHC has been freely sold by internet websites as a “legal” replacement to THC and cannabis in a range of highly attractive branded and unbranded products, some of which are sold as “legal highs”.

Reported opinions describe HHC effects on average comparable to those of Δ⁹-THC (sedation and relaxation, euphoric high and a smooth, calming experience, less energetic and more cerebral) and only sporadic episodes of side effects like psychosis, uncontrolled tremors, and so forth (reddit.com 2023; Schmidt 2023; reddit.com 2023). The intensity of the effects can vary from person to person. Apparently, the majority of users vape it through e-cigarettes or smoke it in herbal matrices but gummies are also reported (reddit.com. 2023; reddit.com. 2023).

10-Hydroxy-hexahydrocannabinol (10-OH-HHC)

(6aR,9R,10S,10aR)-6,6,9-Trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromene-1,10-diol and (6aR,9S,10R,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromene-1,10-diol.

Chemistry and synthesis

It exactly refers to (10S)-hydroxy-(9R)-hexahydrocannabinol, also known as 10α-hydroxy-(9R)-hexahydrocannabinol), a cannabinoid actually isolated from cannabis (Ahmed et al. 2015). It is also a known minor metabolite of HHC (Harvey and Brown 1991)and its structure is known since 1980 when it was first synthesized by Mechoulam (Mechoulam et al. 1980). Companies selling this cannabinoid claim to follow a semi-synthetic route starting from CBD, but they do not give any other information (Future4200 2023).

Pharmacology

Early studies on rhesus monkeys showed that the (10S,9R)- isomer is able to produce psychoactive effects already at 0.5 mg/kg (Mechoulam et al. 1980). No studies are present on its in vitro CB1R binding affinity.

Identification and analysis

Identification and differentiation of isomers can be achieved by GC-MS (both low and high-resolution), LC-MS, and NMR (Cayman 2023). In particular, although MS spectra are very similar, chromatographic retention times are slightly different with both techniques (GC and LC). In LC, with a linear gradient of methanol, the (10R,9S) isomer eluted first. NMR, particularly HMBC, COSY and NOESY, proves to be essential to distinguish axial and equatorial position of atoms.

Recreational use

In the Reddit forums it is stated that the effects are more or less the same as HHC itself, although a bit shorter in duration. Additionally, it is easier to handle as it is a crystalline solid (reddit.com. 2023).

Hexahydrocannabinolic acid (HHCA)

(6aR,9R,10aR)-1-Hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromene-2-carboxylic acid and (6aR,9S,10aR)-1-hydroxy-6,6,9-trimethyl-3-pentyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromene-2-carboxylic acid.

Hexahydrocannabinolic acid (HHCA) is the carboxylic acid analogue of HHC, analogous to THCA in relation to THC. Limited information is available about this cannabinoid, except for its synthesis and practical application. A semi-synthetic process for HHCA has been patented, starting with a crude cannabis essential oil that undergoes hydrogenation (HHCA is indicated as HTHCA) (Scialdone 2016). However, the epimeric composition of the final product is not mentioned.

No literature records are available on the pharmacological activities and analytical methods for the identification and quantification of the carboxylated form. However, it is not intended for use in its current state, as HHCA will undergo decarboxylation upon heating to be converted into HHC, which is the form actually consumed. It appears that the carboxylated species is much more stable than its decarboxylated counterpart, as it exists in a crystalline form, making it easier to handle and avoiding the stickiness associated with a distillate (reddit.com. 2023).

7,8-Dihydrocannabinol (DHC)

6,6,9-Trimethyl-3-pentyl-7,8-dihydrobenzo[c]chromen-1-ol.

DHC is less common on forums and indicates 7,8-dihydrocannabinol with a structure similar to that of Δ⁹-THC but with an additional double bond on the C6a-C10a position (Jagannathan 2020). The semi-synthetic process was described in a patent starting from Δ⁹-THC, which could be easily obtained from CBD (as seen in the above paragraphs), and treating with 3,5-di-tert-butyl-1,2-benzoquinone (Loewinger et al. 2022). The reaction carried out at very low temperature (-40 °C) can afford pure DHC avoiding the formation of CBN, which is thermodynamically more stable (Loewinger et al. 2022).

Although this is expected to have the same pharmacological effects of Δ⁹-THC, it results more reactive to undergo liver metabolism (Jagannathan 2020) and be converted to 11-OH-THC, which is notedly more potent than the parent compound.

Synthetic pseudo-natural cannabinoids

Under this sub-group all Δ⁹-THC homologues can be found, starting from those with different length of the alkyl side chain to their hydrogenated derivatives. All the compounds included in this section are of recent discovery, including the Δ⁹-THC analogues identified by the authors’ group (Linciano et al. 2020a; Linciano 2020b; Citti et al. 2019).

SPNCs, although being naturally occurring, cannot be obtained by a semi-synthetic process starting from CBD or Δ⁹-THC as the elongation of the alkyl side chain is not straightforward starting from these precursors. Therefore, a fully synthetic protocol is required to afford the desired products, generally starting from the resorcinol with the appropriate side chain length. Once the THC analogue is obtained, it can be easily hydrogenated to obtain the corresponding HHC derivative.

All Δ⁹-THC homologues sold for recreational use are generally not tested for purity, thus they can come in either pure Δ⁹ or Δ⁸ form or as a mixture of the two.

For all HHC analogues no scientific literature could be retrieved, only information on their recreational use was rather available.

Δ⁹-Tetrahydrocannabutol (Δ⁹-THCB)

(6aR,10aR)-3-Butyl-6,6,9-trimethyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

Until a few years ago Δ⁹-THCB had only been detected and characterized by means of mass spectrometry in the plant matrix by Harvey in (1976). Then, in 2020 Linciano et al. identified Δ⁹-THCB in samples of C. sativa L., Italian FM2 medicinal variety, and delivered a full characterization through UHPLC-HRMS (Orbitrap), NMR, UV, and circular dichroism spectra (Linciano et al. 2020a).

In order to confirm the exact structure with absolute stereochemistry, the authors performed a stereoselective synthesis starting from a Friedel-Craft allylation of 5-butylbenzene-1,3-diol with (1S,4R)-1-methyl-4-(prop-1-en-2-yl)cycloex-2-enol (pTSA as catalyst). The reaction led to (−)-trans-CBDB, which was turned first into Δ⁹-THCB (not isolable at this step) and then, being more stable, quantitatively into (−)-trans-Δ⁸-THCB. By successive addition and removal of hydrochloric acid (respectively with ZnCl₂ as catalyst and potassium tert-amylate as base), (−)-trans-Δ⁸-THCB was quantitatively converted into (−)-trans-Δ⁹-THCB (91% yield) (Linciano et al. 2020a).

Pharmacology

The only literature records on the pharmacological behaviour of Δ⁹-THCB are available from the work by Linciano et al. that reports both in vitro and in vivo investigation of the cannabimimetic properties of this cannabinoid (Linciano et al. 2020a).

The hCB1R and hCB2R binding affinity was tested in a radioligand test based on the displacement of radiolabeled [³H]CP55940 from hCB1R or [³H]WIN 55212-2 from hCB2R (Linciano et al. 2020a). Compared to Δ⁹-THC, Δ⁹-THCB showed a three-fold higher affinity for hCB1R (K_i = 15 nM for Δ⁹-THCB vs. K_i = 41 nM for Δ⁹-THC) and similar affinity for hCB2R (Linciano et al. 2020a).

In vivo cannabimimetic effects were evaluated through the tetrad tests in mice, which showed only a partial interaction of Δ⁹-THCB with the CB1R in the same fashion as Δ⁹-THC (Linciano et al. 2020a).

Identification and analysis

In order to characterize Δ⁹-THCB, Linciano et al. applied the main traditional techniques (HPLC-HRMS, ¹H and ¹³C NMR, UV spectroscopy) and the more advanced approach based on metabolomics, an innovative tool particularly useful in simultaneously identifying the impressive number of phytocompounds present in C. sativaL (Linciano et al. 2020a).

At the time of writing, unlike what has been done for other cannabinoids, no specifically validated analytical methods for Δ⁹-THCB are described in the literature. It is therefore reasonable to assume that the same approaches are applicable to the analysis of Δ⁹-THCB in commercial products for recreational use, herbal products and biological samples. Indeed, a certificate of analysis of a cannabis food product (chocolate bar) reports a series of cannabinoids including Δ⁹-THCB analysed using a certified HPLC method (detector not specified) (SDPharmLabs 2023).

Recreational use

Δ⁹-THCB is commercially available online as an isolate (declared purity 96,9%) for the business to business market (Pharmabinoid 2023) and as in all other forms already encountered for other cannabinoids (tinctures, gummies and vape liquids) for retail (TheCalmLeaf 2023; Binoid n.d.). To the authors’ knowledge, no investigation has been done on its exact composition (i.e. whether it is pure Δ⁹-THCB or Δ⁸-THCB or a mixture thereof).

By type and duration of effects, users declare that its potency is either comparable to or higher than that of Δ⁹-THC (Brandrup 2023; Future4200 2022). They also refer of quick sensations of euphoria, mental energy and uplift as well as feelings of bodily relaxation and calmness (Brandrup 2023). Moreover, especially long standing users complain about the short duration of the effects and that they are not particularly distinctive in case of developed tolerance (reddit.com. 2023).

Δ⁹-Tetrahydrocannabihexol (Δ⁹-THCH)

(6aR,10aR)-3-Hexyl-6,6,9-trimethyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

Among the homologues of Δ⁹-THC with varying lengths of the alkyl side chain, (−)-trans-Δ⁹-tetrahydrocannabihexol ((−)-trans-Δ⁹-THCH) emerged as the latest addition to the series, completing the spectrum after the discovery of butyl- and heptyl-side chain compounds. Traditionally, it was believed that the biosynthesis of cannabinoids in C. sativaL. could only lead to compounds with an odd number of carbon atoms in the side chain, with even numbers arising from subsequent fungal ω-oxidation (Hanuš et al. 2016). However, recent advances in metabolomics analysis in an untargeted fashion using UHPLC-HRMS and, in particular, UHPLC interfaced to an Orbitrap mass spectrometer with heated electrospray ionization source (UHPLC-HESI-Orbitrap) have enabled a thorough investigation of all compounds, even in trace amounts, in cannabis varieties. In 2020, this technology led to the identification of Δ⁹-THCH in the Italian medicinal variety FM2 (Linciano et al. 2020a).

The identity of (−)-trans-Δ⁹-THCH in FM2 extracts was confirmed through stereoselective in house synthesis, demonstrating a complete overlap of analytical data obtained from UHPLC-HESI-Orbitrap and ¹H and ¹³C NMR spectroscopy. The synthetic pathway involved the condensation of 5-hexyl-resorcinol with (1S,4R)-1-methyl-4-(prop-1-en-2-yl)cycloex-2-enol, catalyzed by pTSA. The initial product is the Δ⁸-THC analogue generated from a CBD intermediate and subsequently converted into its Δ⁹ chlorinated derivative. The latter undergoes selective elimination of the chlorine atom from C9 on the terpene moiety to yield the desired Δ⁹-THC product. Due to the time-consuming nature and low yields of this procedure, the authors stopped the process at the stage where CBDH is still present, preventing the conversion of Δ⁹-THCH into Δ⁸-THCH. Subsequent separation of the two single homologues was achieved through semi-preparative LC (Linciano et al. 2020a).

In the hypothesis that the same production procedure is used to obtain recreational Δ⁹-THCH, it is reasonable that what is labelled as THCH could be a mixture of Δ⁸ and Δ⁹-THCH in varying proportions.

Pharmacology

To the best of the authors’ knowledge, there is no research article in the scientific literature specifically addressing the in vivo or in vitro evaluation of the psychoactive effects of Δ⁹-THCH. However, drawing on information available for related compounds and consumer reports, it is reasonable to consider its interaction with hCB1R as highly likely, given its increased lipophilicity. A comprehensive comparative study, encompassing in vivo and in vitro approaches, of the entire n-alkyl side chain THC series could provide valuable insights into the role of the side chain in receptor interaction.

Brown and Harvey conducted an evaluation of the metabolism of Δ⁸ and Δ⁹-THCH in mice, revealing that their pharmacokinetics are intermediate between those of Δ⁹-THC and Δ⁹-THCP (see next paragraph) (Brown and Harvey 1988). Similar substitution reactions occurred at the same positions as observed for the other two compounds, along with an oxidation of the 11-hydroxyl group to a carboxylic acid. Moreover, they highlighted an additional metabolic pathway leading to poly-hydroxylation on the side chain, a phenomenon not observed before for Δ⁹-THCH and lower homologues (Brown and Harvey 1988).

Identification and analysis

Linciano et al. carried out a semi-quantitative determination of the compound in the extract of the FM2 variety by UHPLC-HESI-Orbitrap MS confirming that, due to its low concentration in the plant, such technique is the most suitable for its detection and identification (Linciano et al. 2020a).

Recreational use

Marketing strategies for Δ⁹-THCH took place as already described for the other compounds listed in this review. Its discovery attracted the attention of both the consumers looking for new legal substances and the industry that has promptly responded with a range of products spanning tinctures, gummies, and liquid for e-cigarettes. Δ⁹-THCH may be the only active compound or it may be blended in a mixture with other cannabinoids (Binoid 2023).

Sometimes online sales sites propose wide informative pages aimed at presenting the new product, describing the differences and similarities with other cannabinoids, with detailed descriptions of the effects on body and mind (DeltaMunchies 2022; Schmidt 2023). In online forums it tends to be compared with Δ⁹-THC and Δ⁹-THCP in terms of potency: while there is obviously a large amount of subjectivity in the consumers’ experience, it is quite often reported that the psychoactive effect lasts longer than that of Δ⁹-THC (reddit.com. 2023).

Δ⁹-Tetrahydrocannabiphorol (Δ⁹-THCP)

(6aR,10aR)-3-Heptyl-6,6,9-trimethyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

Among the about 150 phytocannabinoids produced by Cannabis sativa L., (‒)-trans-Δ⁹-tetrahydrocannabiphorol (Δ⁹-THCP), first identified by Citti et al. in the FM2 cannabis variety (Citti et al. 2019), has quickly gained great attention from both the pharmaceutical industry and consumers for recreational purposes by virtue of its estimated potency. Hence, being one of the most promising known compounds, it is reasonable to expect, in the medium and long term, the appearance on the market of hemp varieties specially selected in order to increase its content.

Δ⁹-THCP can be stereoselectively synthesized by condensation of 5-heptylbenzene-1,3-diol with (1 S,4R)-1-methyl-4-(prop-1-en-2-yl)cycloex-2-enol, using pTSA as catalyst, for 90 min. Final stereoselective yields are influenced by the duration or the diverse Lewis’ acids (Citti et al. 2019).

Pharmacology

Following its discovery, Δ⁹-THCP was immediately studied for its pharmacological effects both in vitro and in vivo. Δ⁹-THCP binds with high affinity to both hCB1R and hCB2R with a Ki of 1.2 and 6.2 nM, respectively. As a result, Δ⁹-THCP in vitro binding affinity resulted 33-fold higher than Δ⁹-THC (Ki = 40 nM), 63-fold higher than Δ⁹-tetrahydrocannabivarin (Δ⁹-THCV, Ki = 75.4 nM) and 13-fold higher than the recently discovered Δ⁹-THCB (Ki = 15 nM) against hCB1R (Linciano et al. 2020a; Citti et al. 2019). In addition, Δ⁹-THCP binding affinity for hCB2R resulted about 5- to 10-times higher (Ki = 6.2 nM) than that of Δ⁹-THC, Δ⁹-THCB, and Δ⁹-THCV, which instead showed a comparable binding affinity with a Kiranging from 36 to 63 nM (Linciano et al. 2020a; Citti et al. 2019).

The cannabimimetic activity in vivo of Δ⁹-THCP was evaluated by the tetrad of behavioural tests on mice, which included the assessment of spontaneous activity, the immobility index (catalepsy), analgesia and changes in rectal temperature. Δ⁹-THCP was found to decrease locomotor activity and rectal temperature, induce catalepsy and produce analgesia miming the properties of a full CB1R agonist using the same dose used for Δ⁹-THC (10 mg/kg). At lower doses, Δ⁹-THCP acted like a partial CB1R agonist like Δ⁹-THC (Citti et al. 2019).

Identification and analysis

Considered its low amount in cannabis extracts, HPLC-HRMS is the optimal technology to identify and quantify Δ⁹-THCP as shown in the first study on this compound (Citti et al. 2019).

Another study examined the interference of isomers and related cannabinoids on the Cannabinoids Direct ELISA kit from Immunalysis, as a non-target, similarly structured compound can generate a positive response (Moody et al. 2022). This research demonstrated that structural isomers, such as Δ⁸-THC and Δ¹⁰-THC, exhibit a higher cross-reactivity than other Δ⁹ counterparts, while Δ⁹-THCP showed minimal cross-reactivity. This brings to the conclusion that despite its pharmacological/psychoactive effects are comparable to Δ⁹-THC even at low doses, the Direct ELISA kit from Immunalysis would not be able to detect Δ⁹-THCP in consumers’ whole blood.

Recreational use

Δ⁹-THCP is freely available for purchase on the web. Despite its supposed positive effects are widely highlighted on the label, disclaimers often state that it is not for human consumption but only for collection or technical use. It is sold spiked on plant matrices, in vape cartridges and in edible products like gummies and tinctures (Vivimu 2023; L’ErbaProibita 2023).

Online it is reported by recreational users that effects could last up to 24 h or more but this information is only indicative as the physical characteristics of the consumer are not specified (sex, weight, age, health conditions and habit to use) nor if the product contained only Δ⁹-THCP or other THC related compounds (reddit.com. 2022).

Hexahydrocannabutol (HHCB)

(6aR,9R,10aR)-3-Butyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol and (6aR,9S,10aR)-3-Butyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol.

No information is available on the synthesis of hexahydrocannabutol (HHCB), though it can be presumed it is derived from hydrogenation of either Δ⁸– or Δ⁹-THCB, thus through a fully synthetic process. Although no details could be retrieved on its epimeric composition, it can be assumed that the synthetic procedure is adjusted to primarily obtain the (9R) epimer, which should be the active one based on the literature reported for standard HHC.

Users on reddit.com report an experience similar to the one tried with hexahydrocannabihexol (HHCH, see next paragraph) when consuming HHCB edibles (reddit.com. 2023). In particular, it has a quick onset of the effects, starting 5 to 15 min after ingestion, to drop just as quickly, thus avoiding the bad side effects generally encompassed the day after (TSM 2023). An informative website reports the effects produced by HHCB including stress reduction, relaxing effect, euphoria, appetite stimulating effect, sleep-inducing effect, and analgesic effect (TSM 2023).

Hexahydrocannabihexol (HHCH)

(6aR,9R,10aR)-3-Hexyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol and (6aR,9S,10aR)-3-Hexyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol.

The same considerations drawn for HHCB could apply to HHCH as no information is available in the literature regarding its synthesis and pharmacology. For the same reason, it is presumed that the active epimer is the (9R).

Reddit users report different experiences, but the majority say that vaping HHCH distillates gives a mild sensation, even at high concentration levels close to 80%, nothing compared to the corresponding Δ⁹-THC hexyl counterpart Δ⁹-THCH (reddit.com. 2023). On the other hand, HHCH edibles produce a high psychoactive effect (reddit.com. 2023).

HHCH can be found in several products including cookies, gummies, and sprayed herbs (reddit.com. 2023).

Hexahydrocannabiphorol (HHCP)

(6aR,9R,10aR)-3-Heptyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol and (6aR,9S,10aR)-3-Heptyl-6,6,9-trimethyl-6a,7,8,9,10,10a-hexahydro-6H-benzo[c]chromen-1-ol.

Chemistry and synthesis

The most feasible synthesis for “illegal” production of hexahydrocannabiphorol (HHCP) seems to be the one reported by Cornia et al. starting from citronellal and 5-heptylresorcinol (sphaerophorol) instead of olivetol and using diethylaluminum chloride as catalyst (Cornia et al. 1989). However, a semi-synthetic approach has also been attempted by hydrogenation of a C. sativa extract previously enriched in Δ⁹-THCP by distillation (Bueno and Greenbaum 2021). More productive and stereoselective synthetic methods would resemble the routes already used in the synthesis of HHC but with an heptyl-substituted resorcinol and (R)-citronellal precursors.

Pharmacology

A dog ataxia assay of the homologous series of THC and HHC run during the 1940s and in 1950 suggested that the “hexyl-” series is dramatically more potent, THCP is slightly more potent, while all the other compounds (hence including HHCP) resulted of weaker effect compared to Δ⁹-THC (Adams et al. 1941; Loewe 1944; Loewe 1950). These studies were affected by an unknown epimeric purity of the analyte so the proposed ranking should be better considered as indicative.

In vitro tests on the CB1R and CB2R have shown great affinity of both Δ⁹-THCP (Citti et al. 2019) and the metabolite-like 11-OH-9β-HHCP (Ujváry 2023) suggesting that the cannabimimetic effects of HHCP ((9R) epimer) would be worth an in-depth evaluation.

Identification and analysis

At present, no specific literature is available on analytical methods for the qualitative and quantitative determination of HHCP. On the basis of its chemical structure the same analytical techniques available for other cannabinoids should be fit for the purpose with either GC or HPLC needed to separate the two epimers. Characterization data for this compound (GC-MS, FT-IR, ¹H NMR, ¹³C APT-NMR, 2D-NMR HSCQ-DEPT, 2D-NMR COSY, 2D-NMR HMBC, 2D-NMR TOCSY, 2D-NMR NOESY were provided to EMCDDA by the Customs Laboratory of Slovenia following the analysis of a seized postal sample (EMCDDA 2023).

Recreational use

On the web HHCP is more advertised by purchasers than reviewed by users probably because it is a relatively new compound on the market following research on the boosting effects of the seven carbon atoms chain on previously known cannabinoids. Though comments on its psychoactive effect seldom refer to the use of the single substance, many users report of unprecedented euphoria and in general intense effects but usually uplifting and providing a solid mood boost (Schmidt 2023).

Online retailers claim HHCP has several benefits including strong mental and body experience, anxiolytic properties, relief, happy experience, better mood, great feelings and good times (HHC-P Effects and Benefits: Why Everyone Loves Them; LAWEEKLY 2022). As for other cannabinoids, they provide it in different forms such as tinctures, vape cartridges, gummies (also in combination with other compounds) (binoid 2023).