Highly potent analgesic activity of monoterpene-derived (2S,4aR,8R,8aR)-2-aryl-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2H-chromene-4,8-diols

New chiral heterocyclic compounds with a hexahydro-2H-chromene framework were synthesized by reactions of (1R,2R,6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol with aromatic aldehydes in the presence of montmorillonite clay. The analgesic activity of the compounds was studied in vivo. The majority of these compounds showed significant analgesic activity in the acetic acid-induced writhing test; the compounds containing one hydroxy and one methoxy substituents also showed analgesic activity in the hot-plate test. (2S,4aR,8R,8aR)-2-(3-Hydroxy-4-methoxyphenyl)-4,7-dimethyl-3,4,4a,5,8,8a-hexahydro-2H-chromene-4,8-diol was as effective as the diclofenac sodium reference taken in the same dose in both tests. It has low acute toxicity and is very promising for further development.