Several Z-and E-methylenecyclopropane nucleoside analogues were synthesized and evaluated for antiviral activity. Reaction of the Z-and E-2-amino-6-chloropurine methylenecyclopropanes with ammonia or cyclopropylamine gave 2,6-diamino or 2-amino-6-cyclopropylamino analogues. Alkylation elimination of N 4 -acetylcytosine with ethyl Z-and E-2-bromo-2-bromomethylcyclopropane-1-carboxylates gave a mixture of the Zand E-methylenecyclopropane derivatives of cytosine. Reduction furnished a mixture of syncytol and the E isomer. Benzoylation led to the respective N 4 -benzoyl derivatives which were separated by chromatography. Debenzoylation afforded pure syncytol and the E isomer. Alkylation of 2,4-bis-O-trimethylsilylthymine with ethyl Z-and E-2-bromo-2-bromomethylcyclopropane-1-carboxylates gave the corresponding Z-and E-1-bromocyclopropylmethylderivatives of thymine. Basecatalysed elimination of HBr gave Z-and E-methylenecyclopropane carboxylic esters. Reduction furnished, after chromatographic separation, synthymol and the E isomer. The Z/E isomeric assignment of the obtained products followed from 1 H NMR spectroscopy. The methylenecyclopropane analogues were tested for antiviral activity in vitro against human and murine cytomegalovirus (HCMV, MCMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV), hepatitis B virus (HBV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpesvirus 6 (HHV-6) and human immunodeficiency virus type 1 (HIV-1). The Z-2-amino-6-cyclopropylaminopurine analogue was the most effective agent against HCMV (EC 50 or EC 90 0.4-2 µM) followed by syncytol and the Z-2,6-diaminopurine analogues (EC 50 or EC 90 3.4-29 and 11-24 µM, respectively). The latter compound was also a strong inhibitor of MCMV (EC 50 0.6 µM). Syncytol was the most potent against EBV (EC 50 <0.41 and 2.5 µM) followed by the Z-2,6-diaminopurine (EC 50 1.5 and 6.9 µM) and the Z-2-amino-6-cyclopropylaminopurine derivative (EC 50 11.8 µM). Syncytol was also most effective against VZV (EC 50 3.6 µM). Activity against HSV-1, HSV-2 and HHV-6 was generally lower; synthymol had an EC 50 of 2 µM against HSV-1 (ELISA) and 1.3 µM against EBV in Daudi cells but was inactive in other assays. The 2-amino-6-cyclopropylamino analogue displayed EC 50 values between 215 and >74 µM in HSV-1 and HSV-2 assays. 2-Amino-6-cyclopropylaminopurine and 2,6-diaminopurine derivatives were effective against HBV (EC 50 2 and 10 µM, respectively), whereas none of the analogues inhibited HIV-1 at a higher virus load. Syncytol and the E isomer were equipotent against EBV in Daudi cells but the E isomer was much less effective in DNA hybridization assays. The E-2,6-diaminopurine analogue and E isomer of synthymol were devoid of antiviral activity.

A series of R and S enantiomers of 2-aminopurine methylenecyclopropane analogues of nucleosides was synthesized. Two diastereoisomeric lipophilic phosphate prodrugs derived from R and S enantiomers of 2,6-diaminopurine analogue were also prepared. Enantioselectivity (diastereoselectivity in case of prodrugs) of in vitro antiviral effects was investigated with human and murine cytomegalovirus (HCMV and MCMV, respectively), herpes simplex virus types 1 and 2 (HSV-1 and HSV-2, respectively), human immunodeficiency virus type 1 (HIV-1), hepatitis B virus (HBV), Epstein-Barr virus (EBV) and varicella zoster virus (VZV). Strong differences in enantioselectivity were found between the R and S enantiomers of adenine analogue and enantiomeric 2-aminopurine analogues. Thus, the enantiomers of adenine analogue were equipotent against HCMV but not MCMV, where the S enantiomer is strongly preferred. The same S preference was found throughout the 2-aminopurine series for both HCMV and MCMV. In contrast, R-synadenol in HIV-1 assays was the best agent, whereas the S enantiomers of moderately effective 2-amino-6-cyclopropylamino and 2-amino-6-methoxypurine analogues were preferred. Little enantiomeric preference was found for R and S enantiomers of synadenol and the corresponding enantiomers of 2,6-diaminopurine analogue against HBV. A mixed pattern of enantioselectivity was observed for EBV depending on the type of host cells and assay. Against VZV, the R and S enantiomers of adenine analogue were equipotent or almost equipotent, but throughout the series of 2-aminopurine analogues a distinct preference for the S enantiomers was found. The stereoselectivity pattern of both diastereoisomeric prodrugs mostly followed enantioselectivity of the parent analogues. The varying enantioselectivities in the series of purine methylenecyclopropane analogues are probably a consequence of differences in the mechanisms of action in different virus/host cell systems.

Synthesis, absolute configuration and antiviral activity of enantiomeric antiviral agents (R)-(-)- and (S)-(+)-synadenol (2 and 3a) are described.