Unnatural enantiomers of 5-azacytidine analogues: Syntheses and enzymatic properties

2'-Deoxy-beta -L-5-azacytidine (L-Decitabine),beta -L-5-azacytidine, and de rivatives were stereospecifically prepared starting from L-ribose or L-xylo se. D- and L-enantiomers of 2'-deoxy-beta -5-azacytidine were weak substrat es of human recombinant deoxycytidine kinase (dCK), whereas both enantiomer s of beta -5-azacytidine or the L-xylo-analogues were not substrates of the enzyme. None of the reported derivatives of beta -L-5-azacytidine was a su bstrate of human recombinant cytidine deaminase (CDA).