Regioselective and efficient synthesis of N 7-substituted adenines, guanines, and 6-mercaptopurines

Study of Direct N7 Regioselective tert-Alkylation of 6-Substituted Purines and Their Modification at Position C6 through O, S, N, and C Substituents

A new N7 direct regioselective method allowing the introduction of tert-alkyl groups into appropriate 6-substituted purine derivatives is developed. This method is based on a reaction of N-trimethylsilylated purines with a tert-alkyl halide using SnCl4 as a catalyst. In this work, we study the structure and optimal reaction conditions leading to the N7 isomer and in some cases also to the N9 isomer. The main goal is devoted to preparing 7-(tert-butyl)-6-chloropurine as a suitable compound for other purine transformations. The stability of the tert-butyl group at the N7 position is tested for classic model reactions, leading to the preparation of new 6,7-disubstituted purine derivatives, which is also interesting from the point of view of possible biological activity.

Design, synthesis, antiviral, and cytostatic evaluation of novel isoxazolidine analogs of homonucleotides

Moderate diastereoselectivities (d.e. 2-62%) of isoxazolidine homonucleotides were observed for cycloadditions between N-methyl-C-(diethoxyphosphoryl)nitrone and N-allyl nucleobases, with trans-isoxazolidines predominating. The stereochemistry of the substituted isoxazolidines was established based on 2D NOE experiments performed for uracil-containing cycloadducts. The cis- and trans-isoxazolidine phosphonates obtained herein were evaluated in vitro for activity against a broad range of DNA and RNA viruses. None of the compounds were endowed with antiviral activity at subtoxic concentrations, but some of them were found to inhibit the proliferation of L1210 cells with IC50 values in the range of 33-100 µM.