Reagent for protection of N, S and particularly O functions as trityl(Trt) derivatives, stable to a wide range of conditions, but readily cleaved by mild acid.  Progressively more acid-labile protecting groups contain one, two or three p-methoxy groups: 4-methoxytrityl chloride, 4,4'-dimethoxytrityl chloride(DMT-Cl) and 4,4',4''-trimethoxytrityl chloride, respectively.  O-tritylation in triethylamine is improved in the presence of catalytic amounts of DMAP[1].  For a one-pot procedure for the high yield, racemisation-free N-tritylation of amino acids, by means of prior in situ O-silylation was reported[2].  N-Trt-derivatives of amino acids have also been converted to Leuch's anhydrides by treatment with phosgene or triphosgene, and the products coupled with amino acid esters to give dipeptides in good yields without racemisation[3].

Ref.

1. Tetrahedron Lett., 95(1979)
2. J.Org.Chem., 47, 1324(1982)
3. J.Org.Chem., 64, 2532(1999)