Design, synthesis, antiviral, and cytostatic evaluation of novel isoxazolidine analogues of C-nucleotides

New Isoxazolidine-Conjugates of Quinazolinones-Synthesis, Antiviral and Cytostatic Activity

A novel series of (3-diethoxyphosphoryl)isoxazolidines substituted at C5 with various quinazolinones have been synthesized by the 1,3-dipolar cycloaddition of N-methyl-C-(diethoxyphosphoryl)nitrone with N3-substitued 2-vinyl-3H-quinazolin-4-ones. All isoxazolidines were assessed for antiviral activity against a broad range of DNA and RNA viruses. Isoxazolidines trans-11f/cis-11f (90:10), trans-11h and trans-11i/cis-11i (97:3) showed weak activity (EC₅₀ = 6.84, 15.29 and 9.44 μM) toward VZV (TK⁺ strain) which was only one order of magnitude lower than that of acyclovir used as a reference drug. Phosphonates trans-11b/cis-11b (90:10), trans-11c, trans-11e/cis-11e (90:10) and trans-11g appeared slightly active toward cytomegalovirus (EC₅₀ = 27–45 μM). Compounds containing benzyl substituents at N3 in the quinazolinone skeleton exhibited slight antiproliferative activity towards the tested immortalized cells with IC₅₀ in the 21–102 μM range.

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.