Synthesis of libraries of thiazole, oxazole and imidazole-based cyclic peptides from azole-based amino acids. A new synthetic approach to bistratamides and didmolamides
作者:Anna Bertram、Nakia Maulucci、Olivia M. New、Siti Mariam Mohd Nor、Gerald Pattenden
DOI:10.1039/b701999h
日期:——
Treatment of a 1 : 1 mixture of the thiazole-based amino acids 8a and 8b with FDPP–i-Pr2NEt in CH3CN gave a mixture of the cyclic trimers 14, 15, 16 and 17 and the cyclic tetramers 19 and 23 in the ratio 2 : 7 : 5 : 8 : 1 : 1 and in a combined yield of 70%. Separate coupling reactions between the bisimidazole amino acid 45 and the thiazole/oxazole amino acids 43a and 42a in the presence of FDPP–i-Pr2NEt led to the bisimidazole based cyclic trimers 55 and 57 respectively (54–57%) and to the cyclic tetramer 56 (8–11%). Similar coupling reactions involving the bisthiazole and bisoxazole amino acids 49 and 47 with the imidazole/oxazole/thiazole amino acids 41a, 42a and 43a gave rise to the library of oxazole, thiazole and imidazole-based cyclic peptides 58, 59, 60, 61, 62, 63, 64 and 65. A coupling reaction between the bisthiazole amino acid 49 and the oxazole amino acid 73 led to an efficient (36% overall) synthesis of bistratamide H (67) found in the ascidian Lissoclinum bistratum. Coupling reactions involving oxazolines with thiazole amino acids were less successful. Thus, a coupling reaction between the phenylalanine-based oxazoline amino acid 71a and either the thiazole amino acid 8a or the bisthiazole amino acid 74 gave only a 2% yield of the cyclic hexapeptide didmolamide A (4) found in the ascidian Didemnum molle. Didmolamide B (68) was obtained in 9% yield from a coupling reaction between 74 and the phenylalanine threonine amino acid 72, using either FDPP or DPPA.
将噻唑类氨基酸8a和8b的1:1混合物与FDPP-i-Pr2NEt在CH3CN中处理,得到了环状三聚体14、15、16和17以及环状四聚体19和23的混合物,其比例为2:7:5:8:1:1,总产率为70%。在FDPP-i-Pr2NEt存在下,双咪唑氨基酸45与噻唑/噁唑氨基酸43a和42a分别进行的单独偶联反应,分别得到了双咪唑基环状三聚体55和57(产率54-57%)以及环状四聚体56(产率8-11%)。类似地,双噻唑和双噁唑氨基酸49和47与咪唑/噁唑/噻唑氨基酸41a、42a和43a进行的偶联反应,生成了噁唑、噻唑和咪唑基环状肽库58、59、60、61、62、63、64和65。双噻唑氨基酸49与噁唑氨基酸73之间的偶联反应,高效(总产率36%)合成了在海鞘Lissoclinum bistratum中发现的双层板H(67)。含有噻唑氨基酸的噁唑啉的偶联反应效果较差。因此,苯丙氨酸基噁唑啉氨基酸71a与噻唑氨基酸8a或双噻唑氨基酸74之间的偶联反应,仅得到了在海鞘Didemnum molle中发现的环状六肽didmolamide A(4),产率仅为2%。使用FDPP或DPPA,从74与苯丙氨酸苏氨酸氨基酸72的偶联反应中获得了产率为9%的didmolamide B(68)。