Novel enzymatic synthesis of levulinyl protected nucleosides useful for solution phase synthesis of oligonucleotides

An efficient synthesis of 3' and 5'-O-levulinyl-2'-deoxy- and 2'-O-alkylribonucleosides has been developed front appropriate nucleosides by enzyme-catalyzed regioselective acylation in organic solvents. Several lipases were screened in combination with acetonoxime levulinate as an acylating agent. Immobilized Pseudomonas cepacia lipase (PSL-C) was selected for acylation of the 3'-hydroxyl group in nucleosides, furnishing 3'-O-levulinylated products 1 and 3 in excellent yields. Similarly, Candida antarctica lipase B (CAL-B) provided 5'-O-levulinyl nucleosides 2 and 4 in high yields. Base-protected cytidine and adenosine analogs were found to be good substrates for lipase-mediated acylations. To demonstrate the industrial utility of this method, 3'-O-levulinyl thymidine and N-2-Ibu-5'-O-levulinyl-2'deoxygunaosine were synthesized on a 25 g scale. Additionally, PSL-C was reused to make the processes further economical. (C) 2003 Elsevier Ltd. All rights reserved.