A One-Pot Tandem Ugi Multicomponent Reaction (MCR)/Click Reaction as an Efficient Protecting-Group-Free Route to 1H-1,2,3-Triazole-Modified a-Amino Acid Derivatives and Peptidomimetics

By a one-pot tandem Ugi multicomponent reaction (MCR)/click reaction sequence not requiring protecting groups, 1H-1,2,3-triazole-modified Ugi-reaction products 6a6n (Scheme 1 and Table 2), 7a7b (Table 4), and 8 (Scheme 2) were synthesized successfully. i.e., terminal, side-chain, or both side-chain and terminal triazole-modified Ugi-reaction products as potential amino acid units for peptide syntheses. Different catalyst systems for the click reaction were examined to find the optimal reaction conditions (Table 1, Scheme 1). Finally, an efficient Ugi MCR+Ugi MCR/click reaction strategy was elaborated in which two Ugi-reaction products were coupled by a click reaction, thus incorporating the triazole fragment into the center of peptidomimetics (Scheme 3). Thus, the Ugi MCR/click reaction sequence is a convenient and simple approach to different 1H-1,2,3-triazole-modified amino acid derivatives and peptidomimetics.