The occurrence of a cyclopropane ring in the side chain constitutes a structural feature unique to marine sterols. The structural types encountered so far range from simple3 (1) and more substituted4t6 (eg, 2 and 3) 22, 23-methylenecholesterols to examples in which the cyclopropane ring arises by bond formation between C24 and C266 (4), C23 and C2874b, c (5) and finally C26 and C27s (6). We now describe still another cyclopropane type-arising ...