Myriam Meléndez-Rodríguez, Carlos M. Cerda-García-Rojas, and Pedro Joseph-Nathan* Quirogane, prenopsane, and patzcuarane skeletons obtained by photochemically induced molecular rearrangements of longipinene derivatives J. Nat. Prod., 2002, 65 (10), pp 1398141. ISSNI:0163-3864 DOI: 10.1021/np020158s
Ultraviolet irradiation of (1R,3S,4S,5S,10R,11R)-1-acetyloxy-7-oxolongipin-8-ene (6), prepared from longipinene diesters isolated from Stevia salicifolia, afforded the new quirogane (7) and prenopsane (8) derivatives, as the major products, together with the minor secondary photoproduct (1R,3R,5R,8S,11S)-1-acetyloxy-7-oxopatzcuar-9-ene (9), which possesses a novel tricyclic sesquiterpene skeleton. The stereostructures of the new compounds 7-9 were mainly determined by NMR techniques including COSY, HSQC, HMBC, and NOESY in combination with molecular modeling obtained by density functional theory calculations. A reaction mechanism accounting for the observed transformations is proposed.