Enantioselective synthesis of α-benzylated lanthionines and related tripeptides for biological incorporation into E. coli peptidoglycan
作者:Thibaut Denoël、Astrid Zervosen、Christian Lemaire、Bernard Joris、Mireille Hervé、Didier Blanot、Guillermo Zaragoza、André Luxen
DOI:10.1039/c4ob01476f
日期:——
The synthesis of modified tripeptides (S)-Ala-γ-(R)-Glu-X, where X = (R,S) or (R,R) diastereomers of α-benzyl or α-(4-azidobenzyl)lanthionine, was carried out. The chemical strategy involved the enantioselective alkylation of a 4-MeO-phenyloxazoline. The reductive opening of the alkylated oxazolines, followed by cyclization and oxidation, led to four PMB-protected sulfamidates. Subsequent PMB removal, Boc protection and regioselective opening with cysteine methyl ester led to protected lanthionines. These compounds were further converted in a one pot process to the corresponding protected tripeptides. After ester and Boc deprotection, the four tripeptides were evaluated as potential analogues of the natural tripeptide (S)-Ala-γ-(R)-Glu-meso-A2pm. These compounds were evaluated for introduction, by means of the biosynthetic recycling pathway, into the peptidoglycan of Escherichia coli. A successful in vitro biosynthesis of UDP-MurNAc-tripeptides from the tripeptides containing α-benzyl lanthionine was achieved using purified murein peptide ligase (Mpl). Bioincorporation into E. coli W7 did not occur under different tested conditions probably due to the bulky benzyl group at the Cα carbon of the C-terminal amino acid.
我们合成了修饰三肽 (S)-Ala-δ-(R)-Glu-X,其中 X = δ-苄基或δ-(4-叠氮基苄基)兰硫鎓的(R,S)或(R,R)非对映异构体。化学策略涉及 4-MeO-苯基噁唑啉的对映选择性烷基化。烷基化的噁唑啉还原开放,然后进行环化和氧化,最终得到四个 PMB 保护的氨基磺酸盐。随后通过去除 PMB、Boc 保护和半胱氨酸甲酯的区域选择性开环,得到了受保护的镧系元素。这些化合物通过一锅法进一步转化为相应的受保护三肽。经过酯和 Boc 去保护后,这四种三肽被评估为天然三肽 (S)-Ala-γ-(R)-Glu-meso-A2pm 的潜在类似物。对这些化合物进行了评估,以便通过生物合成循环途径将其引入大肠杆菌的肽聚糖中。利用纯化的金霉素肽连接酶(Mpl),成功地从含有δ-苄基兰硫氨酸的三肽体外生物合成了 UDP-MurNAc-三肽。在不同的测试条件下,大肠杆菌 W7 都没有发生生物卟啉化,这可能是由于 C 端氨基酸 Cδ 碳上的苄基过大所致。