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Paper | Regular issue | Vol 91, No. 12, 2015, pp.2315-2326
Published online, 27th November, 2015
DOI: 10.3987/COM-15-13333
Synthesis of Novel (S)-N-Boc-3-Pyrazolylalanine-Derived α-Amino Acids

Uroš Grošelj* and Jurij Svete

*Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI – 1000 Ljubljana, Slovenia


Di-tert-butyl (S,E)-4-[(dimethylamino)methylidene]-5-oxopyrrolidine -1,2-dicarboxylate (1), available in three steps from L-pyroglutamic acid, was used as the starting material for the preparation of a small library of N-Boc-protected 3-pyrazolylalanine tert-butyl esters 3 using 'ring-switching' strategy with different hydrazine derivatives 2. Acid-catalyzed deprotection (TFA/CH2Cl2) of 3 yielded free amino acids 4 isolated as dihydrochloride salts, while selective deprotection with HCl/EtOAc furnished N-Boc deprotected tert-butyl esters dihydrochlorides 5. Hydrolysis under basic conditions furnished N-Boc-protected amino acid 6.