Allosamizoline(1)is an aminocyclitol component of allosamidin, a Streptomyces metabolite, and has a cyclopentane ring originated from D-glucosamine. Biosynthesis of the cyclopentane ring was studied by feeding experiments with a variety of deuterium-labeled glucosamine and glucose. In the feeding experiments with [3-2H]-and [4-2H]-D-glucosamine and [1-2H]-D-glucose, deuterium was incorporated into C-3, C-4, and C-1 of 1, respectively. On the other hand, feeding experiments with [5-2H]-and [6, 6-2H2]-D-glucosamine showed that deuterium on C-5 and one of the two deuterium atoms on C-6 of glucosamine were lost during the cyclopentane ring formation of 1. In the feeding experiments with (6R)-and (6S)-[6-2H1]-D-glucose, the (6R)-deuterium of glucose was incorporated into the proS position on C-6 of 1, but the (6S)-deuterium of glucose was not incorporated into 1. These results suggested that an intermediate with a 6-aldehyde group is involved in the biosynthesis of the cyclopentane ring moiety of 1 and overall inversion of stereochemistry of the C-6 methylene group occurred by stereospecific oxidation and reduction on C-6 during the formation of 1. The 6-aldehyde intermediate may play a key role in the biosynthetic step(s) of cyclization to form the cyclopentane ring and/or deoxygenation at C-5.

A new allosamidin analog, termed didemethylallosamidin(3), was isolated from the mycelia of Streptomyces sp. AJ 9463 which is a producer of allosamidin(1)and demethylallosamidin(2). 14C-Labeled 1, 2 and 3 as well as their related compounds, 4, 5, and 6, were prepared to investigate the biosynthesis of 1. Conversion experiments with the labeled allosamidins revealed that 2 was a precursor of 1, but 3 was not incorporated. This suggests that the first N-methyl group is introduced before the cyclization of the aminooxazoline ring during the biosynthesis of 1. Although none of the compounds 4, 5, and 6 were converted to 1, the production of 1 was inhibited by the addition of 4.