Michael V J Ramsay

Expeditious preparation of (−)-2′-deoxy-3′-thiacytidine (3TC)

Abstract The title compound has been prepared in enantiomerically pure form in four steps from (+)-thiolactic acid.

Novel antiparasitic agents derived by modification of a new natural product series

Abstract Regioselective reactions on the C5-, C7- and C23-hydroxyl groups of the macrocyclic lactones (1), (3) and (4) are described.

Unexpected effects of Lewis acids in the synthesis of optically pure 2′-deoxy-3′-oxacytidine nucleoside analogues

Abstract TiCl 4 and SnCl 4 promote the formation of dioxolane nucleosides with racemization in the coupling of enantiomerically pure 2′-deoxy-3′oxaribosides with silylated N -acetylcytosine. The use of TMSOTf, TMSI or TiCl 2 (Oi-Pr) 2 furnishes enantiomerically pure cytosine dioxolane nucleosides in low diastereoselectivity.

Chemical transformations of S541 factors (A)-(D): Preparation au]reactions of the 23-ketones

Abstract The stereoselectivities observed for the reactions of the ketones (5) and (7) with sodium borohydride, Grignard reagents and methoxylamine are described and X-ray data for the oxime (9) are presented.

Chemistry of the herbicidins. Reactivity of silyl enol ethers derived from simple and carbohydrate-based tetrahydropyrans

Details are described of preliminary synthetic studies, based on Lewis acid-mediated alkylation of a silyl enol ether, that were directed towards the C11 glycoside of the herbicidin class of nucleosides. The chemistry presented focuses on limitations encountered with the reactivity of both the electrophilic and nucleophilic components designed to serve this longer term synthetic objective. α-Chloro sulfide 6 readily undergoes a Lewis acid-promoted internal redox reaction leading to sulfide 8; this is a consequence of the O-benzyl protecting group used at C-3 of chloro sulfide 6. This pathway is avoided by use of O-silyl protection, and reaction of the silyl-protected α-chloro sulfide 11 with the simple heterocyclic silyl enol ether 5 gives the herbicidin models 13a and 13b incorporating the required furano-pyrano-pyran skeleton. Further experiments showed that the nucleophilic component required for the herbicidins, the carbohydrate-based silyl enol ether 2, readily underwent Lewis acid-mediated rearrangement to give levoglucosenone 15.

Synthesis of some semi-synthetic nemadectins

The natural product (3) has been modified to provide the semi-synthetic nemadectins (15), (17), and (18).