One-step, stereoselective synthesis of octahydrochromanes via the Prins reaction and their cannabinoid activities

Enantiomeric Isopulegol as the Chiral Pool in the Total Synthesis of Bioactive Agents

Isopulegol, a pool of abundant chiral terpene, has long served as the starting material for the total synthesis of isopulegol-based drugs. As an inexpensive and versatile starting material, this compound continues to serve modern synthetic chemistry. This review highlights the total syntheses of terpenoids in the period from 1980 to 2020 in which with isopulegol applied as a building block.

Novel Machaeriol Analogues as Modulators of Cannabinoid Receptors: Structure-Activity Relationships of (+)-Hexahydrocannabinoids and Their Isoform Selectivities

Machaeriols are an important class of compounds that structurally resemble tetrahydrocannabinol (Δ⁹-THC), with the major differences being inverted stereochemistry at the ring junction as [6aR, 10aR] and an additional stereocenter at the C9 position of the A-ring due to saturation. A previous study reported that machaeriols did not show any cannabinoid receptor activity, even though these hexahydrodibenzopyran analogues mimic a privileged (+)-tetrahydrocannabinoid scaffold. To unravel structural requisites for modulation of cannabinoid receptors, a simple late-stage divergent approach was undertaken to functionalize the machaeriol scaffold using the Suzuki coupling reaction. Fourteen hexahydro analogues were synthesized and screened against both cannabinoid receptor isoforms, CB₁ and CB₂. Interestingly, many of the analogues showed a significant binding affinity for both receptors; however, two analogues, 11H and 11J, were identified as possessing CB₂ receptor-selective functional activity in the GTPγS assay; they were found to be micromolar-range agonists, with EC₅₀ values of 5.7 and 16 μM, respectively. Furthermore, molecular dynamics simulations between the CB₂ receptor and two novel analogues resulted in unique interaction profiles by tightly occupying the active ligand-binding domain of the CB₂ receptor and maintaining stable interactions with the critical residues Phe94, Phe281, and Ser285. For the first time, with the aid of structure-activity relationships of (+)-hexahydrocannabinoids, CB₂ selective agonists were identified with late-stage diversification using palladium-mediated C-C bond formation. By simply switching to (R)-citronellal as a chiral precursor, enantiomerically pure (-)-hexahydrocannabinoids with better CB₁/CB₂ receptor isoform selectivity can be obtained using the current synthetic approach.

Synthesis and Analgesic Activity of Monoterpenoid Aldehyde-derived Hydro-2H-chromeneols

Background:

Despite a variety of drugs used to stop acute pain, problems related to their insufficient efficacy and undesirable side effects have remained unresolved. Therefore, the search for analgesics of new structural types, which combine high activity with low toxicity, is a topical issue. It is known that a number of compounds with a hydrogenated 2H-chromene skeleton exhibit significant analgesic activity in in vivo tests.

Methods:

New hydro-2H-chromenols containing monoterpenoid moieties were obtained via one-pot synthesis by the interaction between para-menthane alcohols and commercially available monoterpene aldehydes: Citral, hydroxycitronellal, myrtenal, and perillaldehyde. The analgesic activity of these compounds wаs studied in the acetic acid-induced writhing test and hot plate test.

Results:

The target compounds were characterized using NMR and HR-MS. Most of them exhibited pronounced analgesic activity.

Conclusion:

Due to high analgesic activity, (2S,4aR,8R,8aR)-2-((E)-2,6-dimethylhepta-1,5-dien-1- yl)-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2H-chromene-4,8-diol is considered as candidate compound to participate in further research.