Benzyloxycarbonyl (Cbz)-amino acid esters were reduced to the corresponding α-aminoaldehydes with diisobutylaluminum hydride. Comparison of specific rotation of the Cbz-aminoalcohols, which were derived from the aldehydes by sodium borohydride reduction, with that of the optically pure material showed that chromatography on a silica gel caused marked racemization in the Cbz-α-aminoaldehyde through keto-enol tautomerism. Cbz-S-Bzl-cysteinal was liable to racemize to a great extent. On the other hand, little racemization occurred in Cbz-NG-nitroargininal. This fact might be accounted for the characteristic cyclic carbinolamine structure of the argininal derivative. The semicarbazones prepared from the crude Cbz-α-aminoaldehydes could be reproduced to the initial aldehydes without racemization. These semicarbazones might be used as good starting materials in peptide aldehyde synthesis.
苄氧羰基(Cbz)
氨基酸酯通过
二异丁基铝
氢化物还原为相应的α-
氨基醛。通过
钠硼氢化物还原得到的Cbz-
氨基醇的特定旋转与光学纯材料的比较表明,在
硅胶上进行色谱分离会显著导致Cbz-α-
氨基醛的变旋现象,这是通过酮-烯醇的互变异构造成的。Cbz-S-Bzl-半胱
氨酸易于显著变旋。另一方面,Cbz-NG-硝基精
氨酸醛的变旋现象很少。这一事实可能与精
氨酸衍
生物特有的环状卡宾醇胺结构有关。由粗制Cbz-α-
氨基醛制备的半卡宾酮可以不发生变旋地再生成为初始的醛。这些半卡宾酮可能作为肽醛合成的良好起始材料。