3,5‐Di‐(tert‐Butyl)‐6‐fluoro‐cycloSal‐d4TMP − A Pronucleotide with a Considerably Improved Masking Group

A new, considerably improved cycloSal masking group has been developed. This new group combines four desirable properties and has been attached to the anti-HIV drug 2′,3′-dideoxy-2′,3′-didehydrothymidine (d4T, 1) to give 3,5-(di-tert-butyl)-6-fluoro-cycloSal-d4TMP (2i). This phosphate triester has a reasonable chemical half-life, highly selectively released d4TMP, has poor − if any − inhibitory effect on butyrylcholinesterase (BChE), and achieved the TK-bypass. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)