D- and L-serine, useful synthons for the synthesis of 24-hydroxyvitamin D3 metabolites.: A formal synthesis of 1α,24R,25-(OH)3-D3,24R,25-(OH)2-D3 and 24S,25-(OH)2-D3

D- and L-Serine have been used for the enantioselective synthesis of tosylates 7a and 7b, useful building blocks for the synthesis of triols 5a and 5b which have already been obtained via a diastereoselective synthesis and used for the synthesis of 2a, 2b and 2c. We have thus performed a formal synthesis of 24S,25-(OH)(2)-D-3, 24R,25-(OH)(2)-D-3 and 1 alpha,24R,25-(OH)(3)-D-3. (c) 2007 Elsevier Ltd. All rights reserved.