Functional group-mediated biotransformation by Curvularia lunata NRRL 2178: synthesis of 3-dehydro-2-deoxy-ecdysteroids from the 3-hydroxy-2-mesyloxy analogues Chatchawan Changtam a , Oratai Sukcharoen b , Boon-ek Yingyongnarongkul a , Nitirat Chimnoi c , Apichart Suksamrarn a, * a Department of Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand b Department of Biotechnology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand c Chulabhorn Research Institute, Vipavadee-Rangsit Highway, Bangkok 10210, Thailand Received 11 August 2007; received in revised form 9 December 2007; accepted 3 January 2008 Available online 12 January 2008 Abstract Microbial transformation of ecdysteroids with 3-hydroxy-2-mesyloxy functional group by the fungus Curvularia lunata NRRL 2178 furnished 3-dehydro-2-deoxy analogues. The metabolites included 3-dehydro-2-deoxy analogues of 20-hydroxyecdysone, pterosterone, pona- sterone A, 20-hydroxyecdysone 20,22-acetonide, shidasterone, and poststerone. The mild biotransformation conditions prevented the metabo- lites from C-5 epimerization. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Ecdysteroid; Biotransformation; 3-Dehydro-2-deoxy-ecdysteroids; Curvularia lunata NRRL 2178 1. Introduction Microbial transformation is the procedure most often em- ployed in regio- and stereoselective synthesis of a compound with a special functionality, which is difficult to carry out by chemical means. 1 The main problem for microbial transforma- tion is to find an appropriate microorganism to react with a cer- tain substrate and the ability of the enzyme to react at the specific position to yield the required product. It is obvious that many strains of bacteria or fungi have to be screened for their capabil- ities to transform each substrate. 2,3 In most cases microorgan- isms of different species produce different metabolites. 4e6 Utilization of microorganisms with the same species but with different strains might lead to different metabolites. For exam- ple, four Aspergillus niger strains (one wild and three UV mutants) biotransformed flavonoids into different metabolites. 7 External factors have also been used to exert some effects on the reaction pathways. For example, changes of the growth media and culture conditions resulted in the bioconversion to different metabolites. 8 The biocatalytic ability of the fungus Beauveria bassiana to metabolize androst-4-en-3,17-dione was modified by controlling the pH of the media and this resulted in the pro- duction of different analogues of the steroid hormone. 9 Addition of some chemicals could alter reaction modes of biotransforma- tion. For example, the biotransformation of taxoids by the fungus Absidia coerulea IFO 4011 in the presence of b-cyclo- dextrin gave a variety of metabolites. 10 The findings provided valuable information for the applications of microbial transfor- mation in organic synthesis. However, prediction of the site of reaction of the substrate and the type of the newly created func- tionality of the metabolite is still with difficulty. An alternative approach of microbial transformation should therefore be pro- posed. It is of interest to investigate whether it is possible to prepare a substrate for a microorganism to react at a specific position and with a required mode of reaction. * Corresponding author. Tel.: þ66 2 3190931; fax: þ66 2 3191900. E-mail addresses: apichart@ram1.ru.ac.th, asuksamrarn@yahoo.com (A. Suksamrarn). 0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2008.01.033 Available online at www.sciencedirect.com Tetrahedron 64 (2008) 2626e2633 www.elsevier.com/locate/tet