Synthesis of Methylenecyclopropane Analogues of Antiviral Nucleoside Phosphonates

Synthesis and antiviral activities of methylenecyclopropane analogs with 6-alkoxy and 6-alkylthio substitutions that exhibit broad-spectrum antiviral activity against human herpesviruses

Methylenecyclopropane nucleosides have been reported to be active against many of the human herpesviruses. The most active compound of this class is cyclopropavir (CPV), which exhibits good antiviral activity against human cytomegalovirus (HCMV), Epstein-Barr virus, both variants of human herpesvirus 6, and human herpesvirus 8. CPV has two hydroxymethyl groups on the methylenecyclopropane ring, but analogs with a single hydroxymethyl group, such as the prototypical (S)-synguanol, are also active and exhibit a broader spectrum of antiviral activity that also includes hepatitis B virus and human immunodeficiency virus. Here, a large set of monohydroxymethyl compounds with ether and thioether substituents at the 6 position of the purine was synthesized and evaluated for antiviral activity against a range of human herpesviruses. Some of these analogs had a broader spectrum of antiviral activity than CPV, in that they also inhibited the replication of herpes simplex viruses 1 and 2 and varicella-zoster virus. Interestingly, the antiviral activity of these compounds appeared to be dependent on the activity of the HCMV UL97 kinase but was relatively unaffected by the absence of thymidine kinase activity in HSV. These data taken together indicate that the mechanism of action of these analogs is distinct from that of CPV. They also suggest that they might be useful as broad-spectrum antiherpesvirus agents and may be effective in the treatment of resistant virus infections.

Synthesis of "reversed" methylenecyclopropane analogues of antiviral phosphonates

Synthesis of "reversed" methylenecyclopropane analogues of nucleoside phosphonates 6a,7a, 6b, and 7b is described. 1-Bromo-1-bromomethylcyclopropane 8 was converted to the bromocyclopropyl phosphonate 9 by Michaelis-Arbuzov reaction with triisopropyl phosphite. Base-catalyzed beta-elimination and deacetylation gave the key Z- and E-hydroxymethylcyclopropyl phosphonates 10 and 11 separated by chromatography. The Mitsunobu type of alkylation of 10 or 11 with adenine or 2-amino-6-chloropurine afforded phosphonates 12a, 12b, 13a, and 13b. Acid hydrolysis furnished the adenine and guanine analogues 6a, 7a, 6b, and 7b. The E and Z configuration was assigned on the basis of NOE experiments with phosphonates 6b and 7b. All Z- and E-isomers were also distinguished by different chemical shifts of CH2O or CH2N (H4 or H4'). Significant differences of the chemical shifts of the cyclopropane C3(3') carbons and coupling constants 3JP,C2(2') or 3JP,C3(3') selective for the Z- or E-isomers were also noted. Phosphonates 6a, 7a, 6b, and 7b are devoid of significant antiviral activity.

Antiviral activities of novel 5-phosphono-pent-2-en-1-yl nucleosides and their alkoxyalkyl phosphonoesters

Three acyclic nucleoside phosphonates are currently approved for clinical use against infections caused by cytomegalovirus (Vistide), hepatitis B virus (Hepsera), and human immunodeficiency virus type 1 (Viread). This important antiviral class inhibits viral polymerases after cellular uptake and conversion to their diphosphates, bypassing the first phosphorylation, which is required for conventional nucleoside antivirals. Small chemical alterations in the acyclic side chain lead to marked differences in antiviral activity and the spectrum of activity of acyclic nucleoside phosphonates against various classes of viral agents. We synthesized a new class of acyclic nucleoside phosphonates based on a 5-phosphono-pent-2-en-1-yl base motif in which the oxygen heteroatom usually present in acyclic nucleoside phosphonates has been replaced with a double bond. Since the intrinsic phosphonate moiety leads to low oral bioavailability and impaired cellular penetration, we also prepared the hexadecyloxypropyl esters of the 5-phosphono-pent-2-en-1-yl nucleosides. Our earlier work showed that this markedly increases antiviral activity and oral bioavailability. Although the 5-phosphono-pent-2-en-1-yl nucleosides themselves were not active, the hexadecyloxypropyl esters were active against DNA viruses and hepatitis B virus, in vitro. Notably, the hexadecyloxypropyl ester of 9-(5-phosphono-pent-2-en-1-yl)-adenine was active against hepatitis B virus mutants resistant to lamivudine, emtricitabine, and adefovir.