Natural Amidines from Microorganisms and Fungi

Recently, Eredenhagen et al. [18] reported the isolation of neoefrapeptins A (6) to N from the culture broth of the strain SID 22 780, identified as Geotrichum candidum Link F. The stmctures were very similar to those of efrapeptins, which contain a bicyclic amidine part at the C-terminus and Aib, Iva and Pip, as well as other unnatural amino acids such as 3-methylproline (3M-Pro) and 1-aminocyclopropanecarboxylic acid (Acc). 

Imada et al. reported the isolation of pyrostatins A and B from culture broth of strain Streptomyces sp. SA-3501 isolated from a marine sediment [19,20]. The structures were determined as 2-iminopyrrolidine carboxylic acid derivatives 7-8. These compounds showed specific inhibitory activity against A-acetylglucosaminidase but no antimicrobial activity. 

Recently, Castellanos et al. [21] reported the isolation of a compound with same structure as pyrostatin B (8) from Caribbean marine sponge Cliona tenuis, however, the spectral data were not identical with those published for pyrostatin B. Total synthesis of the compound with the structure of 8 was achieved to demonstrate that the synthesized 8 was identical with the compound isolated by Castellanos but not with pyrostatin B previously isolated by Imada et al. Further searching of the literature lead to the conclusion that the actual NMR data reported for pyrostatin B matched those of ectoine (9) [22,23], another amidine alkaloid isolated from extremely halophilic species of the bacterial genus Ectothiorhodospira [24]. 

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