Crystallomycin revisited after 60 years: aspartocins B and C.

The study of an archived sample of crystallomycin complex using HPLC, ESI HRMS, and 2D NMR showed that two major components of the antibiotic, compounds 1 and 2, are lipopeptides having the same peptide core, Asp1-cyclo(Dab2-Pip3-MeAsp4-Asp5-Gly6-Asp7-Gly8-Dab9-Val10-Pro11-), N-acylated either with Δ3-iso-tetradecenoyl or Δ3-anteiso-pentadecenoyl that are identical to aspartocins C and B, respectively. According to the 2D NMR study, compound 2 in DMSO solution exists as a mixture of four conformers. The producing strain was identified as Streptomyces griseorubens. Compounds 1 and 2 have considerable Ca2+-dependent activity against Gram-positive bacteria including five MRSA strains.