Total Synthesis of Cyclosporin O Both in Solution and in the Solid Phase Using Novel Thiazolium-, Immonium-, and Pyridinium-Type Coupling Reagents: BEMT, BDMP, and BEP<sup>1</sup>
作者:Peng Li、Jie Cheng Xu
DOI:10.1021/jo991687c
日期:2000.5.1
Cyclosporin O (1), an extensively N-methylated immunosuppressive cyclic undecapeptide isolated from Tolypocladium inflatum Gams, was synthesized in 20-23% overall yield via 4 + 7 segment condensation and cyclization by the combined utilization of novel thiazolium- and immonium-type peptide coupling reagents 2-bromo-3-ethyl-4-methyl thiazolium tetrafluoroborate (BEMT) and 5-(1H-benzotriazol-1-yloxy)-3,4-dihydro-1-methyl 2H-pyrrolium hexachloroantimonate (BDMP) as well as compound 2-bromo-1-ethyl pyridinium tetrafluoroborate (BEP). BEMT and BEP, which have been proven to be very efficient for the coupling of peptide segments containing N-alkylated amino acid residues with respect to the fast reaction speed, low racemization, and high yields, were used to construct hindered amide bonds in CsO with the addition of HOAt, whereas the most efficient HOBt-derived immonium type reagent, BDMP, was used to perform the coupling of coded amino acids in CsO. Thus, the highly hindered protected 8-11 tetrapeptide 25 was successfully synthesized using BEMT in 65% yield, and the 1-7 heptapeptide 21 was obtained in 52-55% yield by the rationally combined utilization of BDMP, BEMT, and BEP. The synthesis of the linear undecapeptide 27 of CsO in the solid phase using BEMT and BEP was accomplished for the further evaluation of the effectiveness of these reagents.
tetrafluoroborate (BEP) was firstly utilized to the synthesis of peptides containing N-methyl amino acid residues both in solution and solid phase, and demonstrated high reactivity, low racemization and excellent yields, which were approved by the successful synthesis of a series of oligopeptides and hindered peptide fragments, such as the 8-11 segment of Cyclosporine A and the pentapeptide moiety of Dolastatin
1-Ethyl 2-Halopyridinium Salts, Highly Efficient Coupling Reagents for Hindered Peptide Synthesis both in Solution and the Solid-Phase
作者:Peng Li、Jie-Cheng Xu
DOI:10.1016/s0040-4020(00)00657-8
日期:2000.10
proved to be very effective for the synthesis of hindered peptides containing N-methylated or Cα,Cα-dialkylated amino acid residues. HPLC monitoring of model reactions indicated that these pyridinium salts demonstrated higher reactivities, lower racemization than the commonly used halogenated uronium and phosphonium salts. The efficiency of these pyridinium type coupling reagents was further proved by the
1-乙基-2-卤代吡啶鎓盐,BEP,FEP,BEPH和FEPH,合成并证明是含有受阻的肽的合成是非常有效的Ñ甲基化的或Ç α,Ç α-二烷基化的氨基酸残基。HPLC对模型反应的监测表明,与通常使用的卤化铀盐和phospho盐相比,这些吡啶鎓盐具有更高的反应活性和更低的消旋性。通过合成一系列受阻的寡肽和活性酯,具有良好的收率和方便的后处理,进一步证明了这些吡啶鎓类偶联剂的效率。使用这些吡啶鎓盐还成功合成了环孢菌素A(CsA)的8-11四肽片段和Dolastatin 15的五肽部分。这些吡啶鎓类偶联剂对SPPS的效率还通过CsA的极受阻碍的8-11肽段和CsO的线性十一肽的固相合成证明。1 H NMR,IR和HPLC。提出主要的反应性中间体是N-保护的氨基酸或肽的相应的酰卤和酰氧基吡啶鎓盐。