[5-(Adenin-9-yl)-5-deoxy-L-pentofuranosyl]phosphonates - A Novel Type of Nucleotide Analogs Related to HPMPA. II. Synthesis of L-ribo and L-xylo Configurated Derivatives by Recyclization of Diethyl (5-RS)-[1,2-O-Isopropylidene-5-O-methanesulfonyl-D-pentofuranos-5-C-yl]phosphonates under Acidic Conditions

Further cyclic analogs of the antiviral (S)-9-(3-hydroxy-2-phosphonomethoxypropyl)adenine (I) were prepared: both anomers of [5-(adenin-9-yl)-5-doxy-L-ribofuranosyl]phosphonic acid (α-IId and β-IId) and [5-(adenin-9-yl)-5-doxy-α-L-ribofuranosyl]phosphonic acid (IIe). Recyclization reaction of diethyl (5RS-(3-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-D-ribofuranos-5-C-yl)phosphonate (IVb) and diethyl (5RS-(3-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-D-xylofuranos-5-C-yl)phosphonate (IVd) in trifluoroacetic acid led to cyclic aldehydes Va and Vb which were reduced to diethyl α- and β-L-ribofuranosylphosphonates VIb and α-L-xylofuranosylphosphonate VIIb. Conversion to the protected 5-O-tosylates VId and VIId, followed by reaction with adenine and deprotection, afforded the mentioned nucleotide analogs IId and IIe. An attempt to prepare L-pentofuranosylphosphonates Vc and XIII, suitable for the synthesis of nucleotide analogs of 3-deoxy-L-erythro and L-xylo configuration (IIf and IIg, respectively) by the recyclization reaction of the corresponding 5-O-methanesulfonyl derivatives IVf and XIIb failed. In this case, anhydro derivatives IXa, XVa and XVIa were isolated and identified.