Reveromycins, new inhibitors of eukaryotic cell growth. III. Structures of reveromycins A, B, C and D.

Reveromycins A, B, C and D are new group inhibitors of the mitogenic activity of epidermal growth factor (EGF), produced by Streptomyces sp.Reveromycinsare novel polyketide type antibiotics which have two terminal carboxylic groups, a spiroketal, a succinate and a varied side chain in the molecule.Determination of their structures by chemical and spectroscopic methods, in particular NMRstudies, is described.Reveromycins A (1), B (2), C (3) and D (4) are novel antibiotics produced by Streptomyces sp.Reveromycins inhibit the mitogenic activity of epidermal growth factor (EGF).The isolation, physico-chemical properties and biological activities are described in preceding papers1'2).In this paper, we report the structural determination of reveromycins A, B, C and D. Reveromycin A (1), [a]£0 -115°, is a white amorphous powder with mp 95°C.It has the molecular formula C36H52O! 1 which was confirmed by elemental analysis and HRFAB-MS m/z 683.3496 (M + Na) + ; calcd 683.3407.The UVspectrum showed the presence of conjugated diene chromophores, lmax (in MeOH) 238 and 260 (sh) nm.In the IR spectrum, broad bands at 3600-3200 and 1690cm"1 were observed and suggested the presence of carboxyl groups.In the SI-MS spectrum, characteristic fragment ions at m/z 643 (MH+-H2O) and m/z 525 (643 -1 18(C4H6O4)) suggested the presence of one hydroxyl group and a succinate moiety.The 13C NMRspectrum (Table 1) exhibited the signals of four carbonyl, ten olefinic carbons, two quaternary carbons, three oxygenated methine, two ordinary methine, ten methylene, and five methyl carbons.The 13C and XHNMR(Table 2) assignments and partial structures (Fig. 1) were established by WHCOSY, ^C^H COSYand heteronuclear multiple-bond correlation (HMBC)3) spectra (Fig. 2).The positions and assignments of four carbonyl carbons and two sp2 carbons (C-8 and C-22) were confirmed by the HMBCspectrum.^-"C long range couplings from H-19 (6 4.51) to C-15 (S 94.9), C-17 (S 23.7) and C-18 (6 82.0) were also observed in HMBCspectrum.The quaternary carbon at 3 94.9 (C-15) suggested the presence of a six-membered spiroketal moiety4).The stereochemistry of three disubstituted double bonds were determined as E configuration from the large coupling constants (/= 15.9 or 15.6Hz).To determine the stereochemistry of two trisubstituted double bonds, NOESY experiments was carried out on trimethyl ester (la).Observed NOEs(Fig.3) between H-7 and H-9, H-lOa (3 2.38) and Me-8, and H-21 and H-23 suggested these double bonds were all E configuration.In NOESY f The Structure of reveromycin A was preliminarily communicated in J. Antibiotics 44, 259~261 (1991).