A New Alkylation-Elimination Method for Synthesis of Antiviral Fluoromethylenecyclopropane Analogues of Nucleosides

Synthesis of 2,2,3-tris(hydroxymethyl)methylenecyclopropane analogues of nucleosides

Synthesis of 2,2,3-tris(hydroxymethyl)methylenecyclopropane analogues 16a, 16b, 17a, and 17b is described. Diethyl ester of Feist's acid 18b was hydroxymethylated via carbanion formation using formaldehyde under simultaneous isomerization to cis diester to give intermediate 19. Reduction followed by acetylation gave triacetate 22. Addition of bromine afforded reagent 23, which was used for alkylation-elimination of adenine and 2-amino-6-chloropurine to provide Z,E-isomeric mixtures of 24a and 24b. Deacetylation and separation furnished the Z-isomers 16a, 16c and E-isomers 17a, 17c. Hydrolytic dechlorination of 16c and 17c gave guanine analogues 16b and 17b. None of the analogues exhibited a significant antiviral activity. Adenosine deaminase is refractory toward adenine analogues 16a and 17a.

9-{[3-fluoro-2-(hydroxymethyl)cyclopropylidene]methyl}adenines and -guanines. Synthesis and antiviral activity of all stereoisomers1

All stereoisomers of adenine and guanine methylene-3-fluoromethylenecyclopropane analogues of nucleosides 9a, 9b, 10a, 10b, 11a, 11b, 12a, and 12b were synthesized and their antiviral activities were evaluated. A highly convergent approach permitted the synthesis of all these analogues using a single intermediate 15. Reaction of aldehyde 13 with fluorotrichloromethane and tri-n-butylphosphine gave fluoroalkenes 14a+14b (83:17). Addition of carbene derived from ethyl diazoacetate gave cyclopropane 15 as the major product. Reduction (19), bromination (20), and phenylselenenylation (21), followed by Se oxidation and beta-elimination gave cis-methylenecyclopropane 22. Addition of bromine provided the reagent 23 for alkylation-elimination. Reaction of 23 with adenine led to an isomeric mixture 25a+26a that after deprotection afforded analogues 9a and 10a. The 2-amino-6-chloropurine furnished 25e+26e and after deblocking (9e and 10e) and hydrolysis gave targets 9b and 10b. Intermediate 15 provided, after debenzylation (27), 2-nitrophenylselenenylation (28), reduction (29), benzylation (30), and oxidation-elimination trans-methylenecyclopropane 31. Addition of bromine gave reagent 32. Further transformations followed the sequence outlined for analogues 9a, 9b, 10a, and 10b. Analogue 9b was effective against human cytomegalovirus (HCMV; Towne) with EC50 2.9 microM. The trans-isomer 10b inhibited AD169 strain of HCMV (EC50 15 microM) and the murine virus MCMV (EC50 2.5 microM). Compound 12a was effective against Epstein-Barr virus (EC50<0.03 microM). Analogue 9a inhibited varicella zoster virus (EC50 5.9 microM) and human immunodeficiency virus type 1 (EC50 5.2 microM). Analogues 9a, 10a, and 11a are moderate substrates for adenosine deaminase. The structure-activity relationships will be discussed in context with other methylenecyclopropane analogues.

Synthesis of Methylenecyclopropane Analogues of Antiviral Nucleoside Phosphonates

Synthesis of methylenecyclopropane analogues of nucleoside phosphonates 6a, 6b, 7a and 7b is described. Cyclopropyl phosphonate 8 was transformed in four steps to methylenecyclopropane phosphonate 16. The latter intermediate was converted in seven steps to the key Z- and E-methylenecyclopropane alcohols 23 and 24 separated by chromatography. Selenoxide eliminations (15 --> 16 and 22 --> 23 + 24) were instrumental in the synthesis. The Z- and E-isomers 23 and 24 were transformed to bromides 25a and 25b which were used for alkylation of adenine and 2-amino-6-chloropurine to give intermediates 26a, 26b, 26c and 26d. Acid hydrolysis provided the adenine and guanine analogues 6a, 6b, 7a and 7b. Phosphonates 6b and 7b are potent inhibitors of replication of Epstein-Barr virus (EBV).