New analogs of rosaramicin isolated from a Micromonospora strain. II. Structure determination.

New 16-membered macrolide antibiotics 6108 Al (1), B (2), C (3) and D (4) were isolated from the culture filtrate of a Micromonosporafastidiosus sp. 1 }. From the physico-chemical, spectroscopic data and chemical degradation studies, these compoundswere shownto be analogs of rosaramicin (5)2), whose structures were different from 5 at the C-18 position. In this paper, we describe the structure elucidation of these compounds. The physico-chemical data of 1 ~4 are summarized in the previous paper1*. The molecular formula of 1 was determined as C33H55N3O9 by HRFABMS (Calcd: m/z 638.4017, Found: m/z 638.4043