Photochemical synthesis of novel dideoxynucleosides

Synthesis of cyclobutane nucleosides 2-preparation of thymine and uracil analogues

1-(2-Oxocyclobutyl-4-benzoyloxymethyl)-2,4(1H,3H)-pyrimidinedione and 1-(2-oxocyclobutyl-4-benzoyloxymethyl)-5-methyl-2,4(1H,3H)-pyrimidinedione can be prepared by reaction of uracil and thymine, respectively, with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both cis and trans isomers with the trans isomer predominating for uracil whereas the trans isomer was the only product which could be isolated for thymine. Both series were subjected to borohydride reduction followed by transesterification with methoxide giving the corresponding uracil and thymine nucleoside analogues. The uracil derivative 1-(2-oxocyclobutyl-4-benzoyloxymethyl)-2,4(1H,3H)-pyrimidinedione was irradiated in aqueous acetonitrile to generate isonucleoside analogues.

Synthesis of cyclobutane nucleosides

2-(6-Chloropurinyl)-3-benzoyloxymethylcyclobutanone can be prepared by reaction of 6-chloropurine with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both N-9 and N-7 regioisomers. Both regioisomers upon hydride reduction followed by aminolysis gave the corresponding adenine nucleoside analogues. However, the N-7 series led to the hypoxanthine analogues as byproducts.

Photochemical synthesis of nucleoside analogues from cyclobutanones: bicyclic and isonucleosides

The preparation of two nucleoside analogues are reported. Both syntheses involve a key photochemical ring-expansion of cyclobutanones to an oxacarbene and its subsequent scavenging by 6-chloropurine. The synthesis of a bicyclic (locked) purine starts from a oxabicycloheptanone with a hydroxymethyl pendant. The preparation of an isonucleoside uses a cyclobutanone with an α-substituted 6-chloropurine. Irradiation of the latter produces an isonucleoside and acyclic nucleoside analogues.

Photochemistry on soluble polymer supports: synthesis of nucleosides

[reaction: see text] A new soluble polymer support synthesis of nucleosides is described. The photochemical ring expansion of cyclobutanones in the presence of poly(ethylene glycol) (PEG) results in polymer-supported ribosides. These photoadducts can be cleaved from the polymer under Vorbrüggen coupling conditions with TMS-protected purines and pyrimidines to give ribonucleosides. The method has been extended to include modified PEGs with dendritic end-groups in order to improve the loading levels for these coupling reactions.