Transient Protection: Efficient One-Flask Syntheses of Protected Deoxynucleosides

Article abstract of DOI:10.1021/ja00369a029

Application of the concept of transient protection to the synthesis of protected deoxynucleosides is described.The deoxynucleosides are first treated with trimethylchlorosilane in pyridine for protection of the hydroxyl groups, and then immediately reacted with an acylating agent - benzoyl chloride for 1a and 1b and isobutyric anhydride for 1c - to effect N-acylation.Hydrolysis of the trimethylsilyl groups takes a few hours in aqueous pyridine or a few minutes with dilute ammonia.The ammonia also effects selective hydrolysis of the initially formed N,N-dibenzoyldeoxyadenosine derivative (3a) to the desired N-benzoyldeoxyadenosine (4a).This one-flask procedure gives crystalline N-acyl deoxynucleosides 4a and 4b in 95percent yield and 4c in 75percent yield, in only a few hours.The 5'-O-dimethoxytrityl deoxynucleosides 8a and 8b are also obtained in a one-flask procedure by initial reaction of the deoxynucleosides with 4,4'-dimethoxytrityl chloride, followed by treatment with trimethylchlorosilane and then benzoyl chloride.Although with deoxycytidine some of the 4-N,5'-O-bis(dimethoxytrityl) derivative (5c) is formed, benzoyl chloride effects conversion to the 4-N-benzoyl derivative (7b).After simple purification by flash chromatography 8a and 8b are each obtained in 80-90percent overall yield from 1a or 1b.