Isolation of anteiso-C₁₇, iso-C₁₇, iso-C₁₆, and iso-C₁₅ Bacillomycin D from Bacillus amyloliquefaciens SD-32 and Their Antifungal Activities against Plant Pathogens

Two new cyclic lipopeptides (3 and 4) were isolated from the culture filtrate of Bacillus amyloliquefaciens strain SD-32, together with two known metabolites, iso-C₁₅ and iso-C₁₆ bacillomycin D (1 and 2). Spectroscopic and chemical analyses identified the structures of the new compounds 3 and 4 as anteiso-C₁₇ bacillomycin D, cyclic (l-Asn-d-Tyr-d-Asn-l-Pro-l-Glu-d-Ser-l-Thr-3-amino-14-methylhexadecanoic acid) and iso-C₁₇ bacillomycin D, cyclic (l-Asn-d-Tyr-d-Asn-l-Pro-l-Glu-d-Ser-l-Thr-3-amino-15-methylhexadecanoic acid), respectively. The absolute configuration of C-3 in the β-amino fatty acid was determined to be R on the basis of the CD spectrum of its dinitrophenyl-p-methoxyaniline derivative. The activities of compounds 1–4 were evaluated against 13 plant pathogens: the activities of anteiso- and iso-C₁₇ bacillomycin D (3 and 4) were almost the same and stronger than those of iso-C₁₅ and iso-C₁₆ bacillomycin D (1 and 2); iso-C₁₅ bacillomycin D (1) was weakest. Compounds 2–4 inhibited the growth of all fungi tested; however, Pythium aphanidermatum was not inhibited at all by any of the compounds. Furthermore, compounds 1–4 at concentrations of 80, 40, 30, and 30 μM, respectively, inhibited completely the Botrytis cinerea infection in cucumber leaf.