6-dioxopiperazin-2-yl]acetate 10 was synthesized in a four-step synthesis. Deprotonation of 10 and subsequent trapping of the first cyclization product led to the bicyclic mixed acetal 13 in 15% yield. The low yield of 13, compared with the yield of the corresponding glutamate derivatives, is explained by the higher energy (strain) of the bicyclo[2.2.2]octane system and the lower conformational flexibility of
从 (S)-
天冬氨酸开始,通过四步合成合成了 (S)-2-[1-allyl-4-(4-methoxybenzyl)-3,6-dioxopapirazin-2-yl]
乙酸甲酯 10。10 的去质子化和随后第一个环化产物的捕获导致双环混合
缩醛 13 的产率为 15%。与相应谷
氨酸衍
生物的产率相比,13 的低产率是由双环[2.2.2]
辛烷系统的较高能量(应变)和较短
乙酸酯侧链的较低构象灵活性来解释的。作为中间体的六元 Na+-螯合物 12 的形成是环化步骤的高非对映选择性的原因。