1H and 13C assignments of two new macrocyclic lactones isolated from Streptomyces sp. 211726 and revised assignments of azalomycins F3a, F4a and F5a.

Azalomycin F(4a) 2-ethylpentyl ester (1) and Azalomycin F(5a) 2-ethylpentyl ester (2), two new macrocyclic lactones, along with three known compounds of Azalomycins F(3a) (3), F(4a) (4) and F(5a) (5), were identified from metabolites of Streptomyces sp. 211726 isolated from mangrove rhizosphere soil. The complete (1)H and (13)C assignments of these compounds were achieved by using (1)H, (13)C, DEPT, HSQC, (1)H-(1)H COSY and HMBC spectra, and the relative stereochemistry of 5 was first elucidated on the basis of proton-proton coupling constants, NOESY and IR spectra. Moreover, some errors in the (1)H and (13)C assignments published of 3, 4 and 5 were found and revised. 1 and 2 were active against Candida albicans, and exhibited moderate cytotoxicity against HCT-116 cell line.