Enzymic acylation of 506U78 (2‐amino‐9‐β‐D‐arabinofuranosyl‐6‐methoxy‐9H‐purine), a powerful new anti‐leukaemic agent

A practical enzymic approach for acylation of 506U78 (2‐amino‐9‐β‐D‐arabinofuranosyl‐6‐methoxy‐9H‐purine), a powerful anti‐leukaemic agent, is described. Novozyme‐435, an immobilized preparation of Candida antarctica lipase, was used to acylate 506U78 regioselectively at the 5′‐position. This rendered the compound more soluble and bioavailable. Vinyl acetate was used as the acyl donor and reactions were carried out in anhydrous 1,4‐dioxane with up to 100 g/l of substrate input. Bioconversions were optimised to achieve impurity (3′‐mono‐ and di‐acetates) levels of less than 0.5%.