A novel ansamycin, rifamycin W, was isolated from a mutant strain of Nocardia mediterranei. The metabolic origin of rifamycin W was studied by 13C nuclear magnetic resonance spectroscopy. Examination of the proton-decoupled pulse and Fourier transform 13C spectra of rifamycin W biogenetically enriched with [1-13C1-, [1-'3C~acetate has revealed that In a previous publication (9) describing the biosynthesis of rifamycin S, we proposed a general scheme for the biogenesis of the ansamycin carbon skeleton in which a single polyketide chain is initiated by a seven carbon amino precursor containing a six-membered ring. According to this scheme, the naphthalenic chromophore, when present, is formed by closure of a second ring including the 2nd, 3rd, and 4th carbons of the polyketide chain, e.g., C-7, C-6, and C-5 in the case of the rifamycins. The results obtained with rifamycin S (9) also implied that a common progenitor might be involved in the formation of the different naphthalenic ansamycins.
1H and 13C NMR spectral studies of lipiarmycin in CDCI , and in pyridine-d; provided evidence for the six partial structures I-VI and the two sugar units 1 and 2. Acid methanolysis led to the isolation of methyl 2-O-methyl-4-O-homodichloroorsellinate-,3-rhamnoside, whose structure was determined by spectroscopic methods.Lipiarmycinl.2) is a chlorine containing antibiotic produced by Actinoplanes deccanensis ATCC 21983, active mainly against Gram-positive bacteria. While the weak in vivo activity delayed further developments, its mechanism of action has been the subject of many studies'-''.In a previous paper2) the preliminary characterization of lipiarmycin was reported, showing the presence of a sugar moiety and of many branched aliphatic chains. Furthermore, homodichloroorsellinic acid was isolated after acid hydrolysis. In this paper we report the structure elucidation of the sugar components and of the two compounds obtained by hydrolysis. In addition, the partial structures of some aliphatic moieties are deduced from 270 MHz 1H and 67.88 MHz 13C NMR spectroscopy.From elemental analysis and osmometric data, supported by 1H and 13C NMR spectroscopy, lipiarmycin has the molecular formula C52H72C1201e-1e• Spectroscopic Studies Fig. 1 shows the IR spectrum of lipiarmycin in CDC13. Absorption bands at 3600, 3560, 3540 and 3500 cm-1 are assigned by deuteration to OH functions, the last three of them being intramolecularly H-bonded. The spectrum shows three carbonyl absorptions at 1730 and 1690 cm-1, unchanged after deuteration, and at 1660 cm-I which shifts to 1640 cm-1 after deuteration.The band at 1690 cm'' is then assigned to a conjugated C=O and that at 1660 cm-1 to a C=O ester conjugated and H-bonded; the band at 1730 cm-1 is due to an aliphatic ester. In the double bond region a band at 1590 cm-1 (1580 cm-I after D,O addition) is associated with an aromatic moiety carrying one or more phenolic groups. These latter functions are confirmed by the presence of 6,0 bands at 1410 and 1220 cm-1 shifted by deuteration. Finally, the strong band at 1070 cm-1 (o _0) can be assigned to the anomeric group of a sugar. Table 1, where the various H-bearing groups are labelled with alphabetical letters. Examination of the 1H NMR data in CDCI, indicates that the total number of protons is 72 of which 5 are exchangeable. Furthermore, the exchangeable H at 5 11.5 is attributed to a phenolic OH
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