Epimerization Induced by a Remote Cationic Center in Potent New Carbapenems.
作者:Hidenori AZAMI、David BARRETT、Toshiyuki CHIBA、Akihiko FUJIKAWA、Kazuo SAKANE、Fumiyuki SHIRAI
DOI:10.1248/cpb.45.209
日期:——
A new, potent 1β-methylcarbapenem (FR21751) containing a novel pyridiniomethylpyrrolidine side chain has been synthesized, and was found to undergo epimerization at the pyrrolidine C-2 position. To investigate this isomerization, we evaluated the epimerization rate by HPLC at various pH values in aqueous solution and the deuterium exchange rate by 1H-NMR spectroscopy in buffered D2O solution. The rate of this epimerization was greater at high pH (≥6), and deuterium exchange occurred only at the benzylic position of the pyridine ring. The results can be interpreted in terms of a mechanism involving anionic and acyclic intermediates. We synthesized the postulated acyclic intermediate of this epimerization independently and demonstrated its cyclization to give a mixture of four diastereomers (6a, 9), in support of our proposed mechanism.
一种新型、强效的1β-甲基碳青霉烯(FR21751)已经合成,它含有一种新型吡啶基甲基吡咯烷侧链,并发现其在吡咯烷C-2位发生异构化。为了研究这种异构化,我们评估了在各种pH值的水溶液中通过HPLC测得的异构化速率,以及通过1H-NMR光谱在缓冲D2O溶液中测得的氘交换速率。这种异构化速率在pH值较高(≥6)时更大,并且氘交换仅发生在吡啶环的苯基位置。这些结果可以用涉及阴离子和非环状中间体的机制来解释。我们独立合成了这种异构化的假定非环状中间体,并证明了它的环化作用,得到四种非对映异构体的混合物(6a、9),从而支持了我们提出的机制。