合成路线1

The second general approach to synthesis of lamivudine does not involve intermediacy of the racemic nucleoside. A variety of routes are available for preparing chiral oxathiolane intermediates which may be coupled to the cytosine base under appropriate conditions where the chirality of the oxathiolane is maintained. Various natural carbohydrate precursors have utility in the synthesis of lamivudine; for example, a synthesis from L-gulose has recently been reported. (+)-Thiolactic acid (XI) has served as a starting material for chiral oxathiolane (XII), which is coupled to silylated cytosine in the presence of TMS-iodide to afford (XIII). Separation of the pure beta-anomer and deprotection affords lamivudine. Alternatively, racemic acid (XV) may be prepared from glyoxylic acid (XIV) and resolution using a suitable chiral base such as norephedrine would afford the chiral acid (XVI), which may be esterified prior to coupling with cytosine to give (XVII) followed by final reduction to lamivudine.

合成路线2