Bicyclo[3.1.0]Hexane Nucleosides

The chemical reorganization of South methanocarbathymidine (S-MCT) produced an excellent substrate for all three kinases: viral HSV-TK and cellular di- and triphosphate kinases. This reorganization changed the South/syn preference of S-MCT that imposes a significant binding penalty in the first phosphorylation step. The rearrangement resulted in the 2′-OH isomer of North methanocarbathymidine, which surprisingly was a better substrate than S-MCT. The study with polymerases confirmed that even for the error-prone and non-essential DNA polymerases, the North sugar pucker and equatorial disposition of the 3′-OH are important for the insertion and extension steps of DNA strands. The North methanocarba 2′-deoxy-adenosine triphosphate (N-MCdATP) corrects the erroneous dGTP:thymidine base pairing of the polymerase ι (hpol ι) due to the strong North/anti association imposed by the bicyclo[3.1.0]hexane template that mimics the mutagenic arrangement of the dGTP:thymidine pairing preferred by hpol ι. On the opposite side, the South sugar puckers create an additional barrier responsible for the rejection of ribonucleotide triphosphate (rNTPs) by DNA polymerases. The metabolic pathways of N-MCT, its pharmacodynamics, and the in vitro and in vivo antiviral activity data led to its selection as a clinical candidate.