The present invention relates to a process for the preparation of Carbamic acid, N-[(1S,2R)-3-[[(4-aminophenyl)sulfonyl] (2-methylpropyl) amino]-2-hydroxy-l-(phenylmethyl)propyl]-, (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester. It further relates to a process for preparation of novel intermediate and their use i...