Lin CY, Chakraborty S, Wong CW, Tai DF. Controversy of Peptide Cyclization from Tripeptide.
Molecules 2021;
26:molecules26020389. [PMID:
33451079 PMCID:
PMC7828492 DOI:
10.3390/molecules26020389]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 01/05/2021] [Accepted: 01/05/2021] [Indexed: 11/18/2022] Open
Abstract
The present investigation reports an attempt to synthesize naturally occurring α-cyclic tripeptide cyclo(Gly-l-Pro-l-Glu) 1, [cyclo(GPE)], previously isolated from the Ruegeria strain of bacteria with marine sponge Suberites domuncula. Three linear precursors, Boc-GPE(OBn)2, Boc-PE(OBn)G and Boc-E(OBn)GP, were synthesized using a solution phase peptide coupling protocol. Although cyclo(GPE) 1 was our original target, all precursors were dimerized and cyclized at 0 °C with high dilution to form corresponding α-cyclic hexapeptide, cyclo(GPE(OBn))27, which was then converted to cyclic hexapeptide cyclo(GPE)22. Cyclization at higher temperature induced racemization and gave cyclic tripeptide cyclo(GPDE(OBn)) 9. Structure characteristics of the newly synthesized cyclopeptides were determined using 1H-NMR, 13C-NMR and high-resolution mass spectrometry. The chemical shift values of carbonyls of 2 and 7 are larger than 170 ppm, indicating the formation of a cyclic hexapeptide.
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