Bithiazole Metabolites from the Myxobacterium Myxococcus fulvus

Abstract

The myxobacteria have produced a wide variety of structurally unique secondary metabolites.1) Of the myxobacteriaderived metabolites, bithiazole-containing compounds e.g. myxothiazoles, [2][3][4] cystothiazoles, 5,6) and melithiazoles, 7) exhibit potent antimicrobial activity, cytotoxicity and inhibition of mitochondrial respiration which have attracted considerable attention for synthetic, biochemical, and related studies. [8][9][10][11][12][13] During the course of our search for bioactive compounds from myxobacteria of Korean soil, we collected a strain of Myxococcus fulvus (strain number JW484) whose crude organic extract exhibited significant cytotoxicity toward the mouse fibroblast cell-line L929. The culture broth of this strain contained several compounds containing a bithiazole moiety as a common structural feature. Herein we describe the isolation, structure determination, and bioactivity of two new compounds of the myxothiazole class.Isolation and fermentation of the microbial strain was carried out following the procedure reported elsewhere.14) The organic extracts from the culture broth and cell mass were prepared by solvent partitioning. Guided by the results of cytotoxicity test and 1 H-NMR analyses, the moderately polar fractions were separated by silica and ODS vacuum flash chromatography followed by ODS HPLC to yield compounds 1-4 as white amorphous solids.Compound 1, the major component, was elucidated to be myxothiazole A, previously isolated from Myxococcus fulvus collected from a tropical soil sample.2,3) The 1 H-and 13 C-NMR data of this compound were in good agreement with those reported previously.The structure of a minor component, compound 2, was also identified to be desmethylmyxothiazole, a derivative of myxothiazole A having a b-diketo functionality, on the basis of combined spectroscopic methods. This compound was previously reported as a synthetic analog of myxothiazole.3)The molecular formula of compound 3 was deduced as C 25 H 33 N 3 O 3 S 2 by combined HR-FAB-MS and 13 C-NMR analyses. The spectral data for this compound were very similar to those obtained for 1. However, detailed examination of the 13 C-NMR data revealed that carbon signals at C-17 and vicinity were considerably shifted from those of 1 (Table 1); d 132.5, 131.8, 126.5, 142.4, and 31.1 for C-15-C-19, respectively, in 1. Corresponding differences were also observed in the 1 H-NMR spectra in which the chemical shifts of H-15-H-19 as well as the coupling constant between H-17 and H-18 were changed noticeably; d 5.80, 6.19, 6.03, 5.69, and 2.35 for H-15-H-19, respectively, J 17,18 ϭ15.2 Hz in 1. These differences were readily accommodated by the configurational change of the C-17 double bond from E to Z that was supported by HMBC experiments. The relative configurations at the C-4, C-5, and C-14 of 2 were assigned to be identical to those of 1 as previously determined by chemical reaction and spectroscopic methods because the chemical shifts of carbons and protons at these asymmetric centers and vicinity of 3 were v...

Characterization of Polyketide Synthase Machinery from the pks Island Facilitates Isolation of a Candidate Precolibactin

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An Overview of the Synthesis and Antimicrobial, Antiprotozoal, and Antitumor Activity of Thiazole and Bisthiazole Derivatives

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