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Lamivudine was developed as the sulfur analogue of zalcitabine (see table 2).  It was initially synthesized as a racemic mixture (BCH-189) and analysis showed that both positive and negative enantiomers of BCH-189 (2',3'-dideoxy-3'-thiacytidine) had in vitro activity against HIV. Lamivudine is the negative enantiomer and is a pyrimidine nucleoside analogue. The 3' carbon of the ribose ring of 2'-deoxycytidine has been replaced by a sulfur atom because it had greater anti-HIV activity and is less toxic than the positive enantiomer.
Lamivudine [(-)β-L-2’,3’-dideoxy-3’-thiacytidine (3TC)] (Figure 1A) has anti-HIV and anti-HBV properties. It was approved in 1998 by the FDA for the treatment of chronic hepatitis B infections. Lamivudine (Epivir-HBV® or Zeffix®) is administered daily at an oral dose of 100 mg. Within the cell, 3TC is converted to its active form [3TC-triphosphate (3TC-TP)] .