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Cu(I) catalyzed [3+2] cycloaddition of in situ generated N-Fmoc/Boc/Z-protected amino alkyl nitrile oxide with propiolic acid has led to a new class of 3,5-disubstituted isoxazole-bearing amino acid derivatives. The click chemistry protocol described herein is efficient in furnishing the isoxazole embedded amino acids. These unnatural synthons were subjected to chain extension on N- as well as C-termini to obtain 3,5-disubstituted isoxazole bearing di and tripeptidomimetics. [ABSTRACT FROM AUTHOR]

A facile one-pot procedure for the synthesis of urea-linked peptidomimetics and neoglycopeptides under Curtius rearrangement conditions employing Deoxo-Fluor and TMSN3 is described. The method is efficient and circumvents the isolation of acyl azide and isocyanate intermediates. The rearrangement of the in situ generated acyl azide via the acyl fluoride was carried out under ultrasonication followed by amine capture to insert a urea bond. The protocol worked well with all the common N-urethane-protected amino acids and also with a sugar-6-acid. [ABSTRACT FROM AUTHOR]

A new class of 1,4-substituted 1,2,3-triazole-based unnatural amino acids is demonstrated by employing click reaction between N-Fmoc amino alkyl azides and propiolic acid. The resulting unnatural amino acids were isolated and then subjected to Fmoc deprotection to isolate 1,2,3-triazole based amino acids as stable solids. These new class of molecules were also used for chain extension from both N- and C-terminals to synthesize dipeptidomimetics bearing 1,2,3-triazole moiety in the backbone.

Application of the Lossen rearrangement to the synthesis of N-urethane protected alpha-peptidyl ureas and ureidopeptides is reported. The carbodiimide mediated rearrangement of N-Boc/Z/Fmoc protected alpha-amino/peptide hydroxamic acids into isocyanates and coupling of the latter with the amino acid esters/peptide esters have been accomplished in a single-pot to obtain good yields of urea products. Synthesis of the ureidoalanine derivatives via the hydroxamate derivatives of N-protected aspartic acid has also been carried out using the same procedure.

Cyclosporin O (CyO), an immunosuppressent cyclic undecapeptide, was synthesized by convergent approach employing Bsmoc-Nmethyl amino acid fluorides and Potassium Salt of 7-Aza-1-hydroxybenzotriazole (KOAt) in solution by stepwise assembly. The couplings were found to be epimerisation free. The difficulty in the coupling of four consecutive N-methyl amino acids at position 8, 9, 10 and 11 was overcome by repeating the coupling thrice at these critical positions. All the ten protected peptide fragments of CyO starting from the dipeptide to the undecapeptide and final protected as well as CyO were isolated and fully characterized.

An epimerization free and efficient total synthesis of immunosuppressant cyclosporin O (CsO) by step-by-step assembly of amino acids in solution phase is reported. The couplings were performed by employing Fmoc-amino acid chlorides and were mediated by zinc dust under neutral conditions. The yield and purity of the coupling of sterically hindered N-methylamino acids to N-methylamino acids at positions 8, 9, 10, and 11 were enhanced by repeating the coupling thrice at these particular junctures. All the 10 intermediate peptides pertaining to CsO and the final CsO were isolated and completely characterized through IR, 1H NMR, mass spectrometry, and HPLC techniques.