Epostatin, new inhibitor of dipeptidyl peptidase II, produced by streptomyces sp. MJ995-OF5 II. Structure elucidation.

During the course of screening fermentation broths for new inhibitors of dipeptidyl peptidase II (EC 3.4.14.2), we discovered epostatin (C23H33N3O5) from Streptomyces sp. MJ995-OF5. The taxonomy of producing strain, fermentation, isolation, physico-chemical properties and biological properties have been described in the preceding paper1). Herein we report on the structure determination of epostatin (Fig. 1) on the basis of spectroscopic studies. The molecular weight of epostatin was measured by FAB-MS (m/z 432 [M+H+], m/z 430 [M-H-]), and the molecular formula of C23H33N3O5 was determined by interpretation of the HRFAB-MS, NMR spectral analyses and elemental analysis1). The structure of epostatin was elucidated on the basis of 1D and 2D NMR experiments in DMSO-d6. In the 1H NMR spectrum, one methyl, eight methylene and four methine, five olefinic and three of five exchangeable protons were observed. The 13C NMR spectrum showed twenty-three carbon signals, and analysis of the DEPT experiment revealed that the 13C NMR signals consisted of fourteen sp3 including one quarternary carbon, six sp 2 and three carbonyl carbons. Signals of six olefinic carbons indicated the presence of three double bonds in epostatin. These and the three carbonyl carbons account for six degrees of unsaturation, so the remaining three degrees of unsaturation should be due to the presence of three rings in the molecule. The carbons bearing protons were assigned by the Heteronuclear Single Quantum Coherence (HSQC) experiment. The 1H and 13C NMR data for epostatin are summarized in Table 1. Analysis of the 1H-1H COSY experiment revealed