- Synthetic approaches to peptides containing the l-Gln-l-Val-D(S)-Dmt motif
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The pseudoprolines S-Dmo (5,5-dimethyl-4-oxaproline) and R-Dmt (5,5-dimethyl-4-thiaproline) have been used to study the effects of forcing a fully cis conformation in peptides. Synthesis of peptides containing these (which have the same configuration as l-Pro) is straightforward. However, synthesis of peptides containing S-Dmt is difficult, owing to the rapid cyclisation of l-Aaa-S-Dmt amides and esters to form the corresponding diketopiperazines (DKP); thus the intermediacy of l-Aaa-S-Dmt amides and esters must be avoided in the synthetic sequence. Peptides containing the l-Gln-l-Val-D(S)-Dmt motif are particularly difficult, owing to the insolubility of coupling partners containing Gln. Introduction of Gln as N-Boc-pyroglutamate overcame the latter difficulty and the dipeptide active ester BocPygValOC6F5 coupled in good yield with S-DmtOH. BocPygVal-S- DmtNH(CH2)2C6H4NO2 was converted quantitatively to BocGlnVal-S-DmtNH(CH2)2C6H4NO2 with ammonia, demonstrating the utility of this approach. Two peptide derivatives (CbzSerLysLeuGlnVal-S-DmtNH(CH2)2C6H4NO2 and CbzSerSerLysLeuGlnVal-S- DmtNH(CH2)2C6H4NO2) were assembled, using these new methods of coupling a dipeptide acid active ester with S-DmtOH and introduction of Gln as Pyg, followed by conventional peptide couplings. The presence of the Val caused these peptides to be cleaved very slowly by prostate-specific antigen (PSA) at Leu ↓ Gln, rather than the expected Gln ↓ Val.
- Suaifan, Ghadeer A.R.Y.,Arafat, Tawfiq,Threadgill, Michael D.
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p. 3474 - 3488
(2008/02/05)
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- Synthesis of aryl esters of protected amino acids from aryl sulfonates
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Aryl esters of Boc- and Fmoc-protected amino acids derived from electron-deficient phenols have been prepared in good yields from aryl 4- nitrobenzenesulfonates in the presence of 1-hydroxy-benzotriazole as catalyst.
- Pudhom, Khanitha,Vilaivan, Tirayut
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p. 5939 - 5942
(2007/10/03)
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- PREPARATION OF PENTAFLUOROPHENYL ESTERS OF FMOC PROTECTED AMINO ACIDS WITH PENTAFLUOROPHENYL TRIFLUOROACETATE
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A high yield procedure for the preparation of pentafluorophenyl esters of Nα-9-fluorenylmethyloxycarbonyl protected amino acids is described.The procedure utilizes pentafluorophenyl trifluoroacetate.
- Green, Michael,Berman, Judd
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p. 5851 - 5852
(2007/10/02)
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- 9-Fluorenylmethyl Pentafluorophenyl Carbonate as a Useful Reagent for the Preparation of N-9-Fluorenylmethyloxycarbonylamino Acids and their Pentafluorophenyl Esters
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9-Fluorenylmethyl pentafluorophenyl carbonate is a useful reagent for the efficient, side reaction-free introduction of N-9-fluorenylmethyloxycarbonyl protecting group into amino acids and for the subsequent preparation of their pentafluorophenyl esters.Some new compounds of both types are described.
- Schoen, Istvan,Kisfaludy, Lajos
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p. 303 - 305
(2007/10/02)
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