Structure elucidation and biosynthesis of 31-methylhopanoids from Acetobacter europaeus. Studies on a new series of bacterial triterpenoids.

Apart from a mixture of bacteriohopanetetrols already found in other Acetobacter species, four new 3 beta-methylhopanoids have been isolated from Acetobacter europaeus. All of them present an ether linkage between a bacteriohopanetetrol or a bacteriohopanepentol and a carbapseudopentose moiety often found in bacterial hopanoids. Three of these ethers were shown by comparison with synthetic reference hopanoids to posess a supplementary methyl group at C31. This novel series of methylhopanoids may be the precursor of yet unidentified molecular fossils found in sediments. [methyl-2H3]Methionine was efficiently incorporated into the 31-methylhopanoids with retention of all three deuterium atoms in the transferred methyl group. This labelling pattern might be consistent with a rather rarely found methylation reaction of an enol.