Rifamycin W Analogues from Amycolatopsis mediterranei S699 Δrif-orf5 Strain

Rifamycin W, the most predominant intermediate in the biosynthesis of rifamycin, needs to undergo polyketide backbone rearrangement to produce rifamycin B via an oxidative cleavage of the C-12/C-29 double bond. However, the mechanism of this putative oxidative cleavage has not been characterized yet. Rif-Orf5 (a putative cytochrome P450 monooxygenase) was proposed to be involved in the cleavage of this olefinic moiety of rifamycin W. In this study, the mutant strain Amycolatopsis mediterranei S699 Δrif-orf5 was constructed by in-frame deleting the rif-orf5 gene to afford thirteen rifamycin W congeners (1–13) including seven new ones (1–7). Their structures were elucidated by extensive analysis of 1D and 2D NMR spectroscopic data and high-resolution ESI mass spectra. Presumably, compounds 1–4 were derivatized from rifamycin W via C-5/C-11 retro-Claisen cleavage, and compounds 1–3, 9 and 10 featured a hemiacetal. Compounds 5–7 and 11 showed oxygenations at various sites of the ansa chain. In addition, compounds 1–3 exhibited antibacterial activity against Staphylococcus aureus with minimal inhibitory concentration (MIC) values of 5, 40 and 0.5 µg/mL, respectively. Compounds 1 and 3 showed modest antiproliferative activity against HeLa and Caco-2 cells with half maximal inhibitory concentration (IC50) values of about 50 µM.

Improved Rifamycin B Production byNocardia mediterraneiMTCC 14 under Solid-State Fermentation through Process Optimization

Optimization of various production parameters using response surface methodology (RSM) was performed to assess maximum yield of rifamycin B fromNocardia mediterraneiMTCC 14. Plackett-Burman design test was applied to determine the significant effects of various production parameters such as glucose, maltose, ribose, galactose, beef extract, peanut meal, ammonium chloride, ammonium sulphate, barbital, pH, and moisture content on production of rifamycin B. Among the eleven variables tested, galactose, ribose, glucose, and pH were found to have significant effect on rifamycin B production. Optimum levels of the significant variables were decided by using a central composite design. The most appropriate condition for production of rifamycin B was found to be a single step production at galactose (8% w/w), ribose (3% w/w), glucose (9% w/w), and pH (7.0). At these optimum production parameters, the maximum yield of rifamycin B obtained experimentally (9.87 g/kgds dry sunflower oil cake) was found to be very close to its predicted value of 10.35 g/kgds dry sunflower oil cake. The mathematical model developed was found to fit greatly with the experimental data of rifamycin B production.