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A mixture of hexafluoroisopropanol-dichloromethane (1 : 4 v/v) acts as a fast, effective and convenient reagent for cleaving protected peptide fragments with a minimal amount of racemization from 2-chlorotrityl chloride resin.

A sequential procedure has been developed whereby neutral amino acids 1 were tritylated via their corresponding trimethylsilyl esters 2 to afford, after mild hydrolysis, IV-trityl amino acids 3 in high yields and purity. Hydroxy amino acids 4 were preferentially tritylated at the amino function by using either Me3SiCl or Me^iCtj (or Ph^iCy for temporary protection of the hydroxy and carboxyl groups. Finally, !Vim-tritylhistidine (9c) was prepared in 97% yield with the aid of the Me2SiCl2, whereas the use of Me3SiCl produced, after tritylation, IV"-tritylhistidine (9b) and 9c in almost equimolar amounts.It is well-known that the trityl moiety as an a-amino protecting group in peptide synthesis can be selectively removed, under extremely mild acidic conditions2, in the presence of other acid-sensitive protecting group.3 In addition, racemization during the coupling step using IV-trityl amino acids is expected to be lower in comparison to otherwise N-protected amino acids.However, the application of the trityl function in peptide synthesis is limited because of the low yields in the prep-aration2,4 of IV-trityl amino acids and their failure, with a few exceptions,2 to couple with other amino acids in acceptable yields.2 While the latter obstacle has been overcome, when dicyclohexylcarbodiimide, mediated with 1-hydroxybenzotriazole, was used as the coupling agent,5 the facile preparation of IV-trityl amino acids remains to be a serious problem.The present synthesis readily provides IV-trityl amino acids in high yields by an experimentally simple "one-pot" procedure involving tritylation of silylated esters of amino acids followed by mild cleavage of the susceptible oxygen-silicon bond.

3[cm-'] = 990 (vs, sheath), 890 (s, cube) (v(V=O,..,)); 745 (s), 615 (vs) (v,,(V-0-V)). 86.36(3), y =76.83(3)", V = 4914(3) lo6 pm3, Z = 2, e,sl.d = 2.57 g cm-'; solution by direct methods, R = 0.083 for 8551 independent reflections (Fo > 4a(Fo)). Some V centers show a transition from distorted squarepyramidal to distorted tetrahedral coordination with an additional longer bond and four show to a lesser extent a disorder of pyramids and distorted tetrahedra. K,(NEt,H), [V,,O,,] 8H,O, also prepared by us, does not show this disorder, but a very strong unresolvable disorder in the cation/ water of crystallization lattice. Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository number CSD-55095, the names of the authors, and the journal citation. [4] a) M. T. Pope, A. Miiller, Angew. Chem. 103 (1991) 56; Angew. Chem. Int. Ed. Engl. 30 (1991) 34; b) A. Miiller, M. Penk, R. Rohlfing, E. Krickemeyer, J. Doring, ibid. 102 (1990) 927 and 29 (1990) 926, and references cited therein; c) A. Miiller, J. Doring, H. Bogge, J. Chem. Soc. Chem. Commun. 1991,273. The bond valence sums for the V atoms were calculated using the expression x n t = ~(d(V-0,)/178)-5.15 (cf. I.

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