Thiomarinols B and C,New Antimicrobial Antibiotics Produced by a Marine Bacterium.

In our previous papers, wereported the structure and stereochemistry of thiomarinol A (previously referred to as thiomarinol)1'2*, produced by a marine bacterium, Alteromonas rava sp.nov.SANK733903), which has antimicrobial activity against Gram-positive and Gramnegative bacteria.Thiomarinol A (TMA) is a hybrid antibiotic composed of a pseudomonic acid analogue and holothin.In this paper we report the isolation, structure elucidation and antimicrobial activities of new thiomarinol derivatives, thiomarinols B (TMB)4) and C (TMC)5).TMAwas isolated from EtOAc extracts of culture broth of SANK733901).TMBand TMCwere separated from the residue containing minor components, obtained from the extracts by removing TMAon column chromatography with silica gel.The residue was dissolved in methanol and applied on preparative HPLC, using a reverse phase column (Senshu-Pak, ODS, H-4251, 10 x 250mm) and developed with 40% CH3CN at a flow rate of 5ml/minutes.Twomain peaks were collected, and TMBand TMCwere obtained as yellow powders by condensation in vacuo, and lyophilization.The physico-chemical properties of TMBand TMC are summarized in Table 1.Oncomparison of the molecular formulae ofTMA(1) and TMB(2), 2 was found to have two more oxygen atoms than 1.The *H and 13C NMRspectra of2 were closely similar to those of 1.However, the chemical shifts of the two sp2 carbons at C-3" and C-4" in the holothin part of2 were different from those of 1.The UVabsorption of 2 was also different from that of 1.These