Synthesis of the 4-methyl-1,2-oxazetidine-4-carboxylic acid moiety of the originally proposed halipeptin A and B structures
作者:Barry B Snider、Jeremy R Duvall
DOI:10.1016/s0040-4039(03)00542-2
日期:2003.4
O-Alkylation of N-hydroxycarbamate 6 with iodo ester 5 affords 15, which was elaborated to mesylate 4. Intramolecular N-alkylation affords methyl N-Boc-4-methyl-1,2-oxazetidine-4-carboxylate (3). The geminal coupling constant of the methylene protons is 8.5 Hz, which is much smaller than the 12.0 Hz reported for halipeptins A and B. This confirms that the halipeptins do not contain an oxazetidinecarboxylic
N-羟基氨基甲酸酯6与碘代酯5的O-烷基化反应得到15,其被精制为甲磺酸酯4。分子内的N-烷基化得到N -Boc-4-甲基-1,2-恶唑烷-4-羧酸甲酯(3)。亚甲基质子的双键偶合常数为8.5 Hz,远小于卤代肽A和B报道的12.0 Hz。这证实了卤代肽不含结构1最初提出的恶唑烷羧酸,而是噻唑啉。修改后的结构2。5的异常O-烷基化 可能是通过电子转移机制进行的。