Isolation and structure determination of cryptophycins 38, 326, and 327 from the terrestrial cyanobacterium Nostoc sp. GSV 224.

Cryptophycin-38 (2), -326 (3), and -327 (4) are three new trace constituents of the terrestrial cyanobacterium Nostoc sp. GSV 224. Cryptophycin-38 is a stereoisomer of cryptophycin-1 (1) and to date is the only naturally occurring analogue that possesses a S,S epoxide group in unit A. Cryptophycin-327 is a geometric isomer that differs from 1 in having a cis Delta(2)-double bond in unit A. Cryptophycin-326 is related to cryptophycin-21, but has two chlorines ortho to the methoxy group in unit B. The relative and absolute stereochemistries of 2 have been related to known cryptophycins by semisynthesis and/or spectral analysis.