A Facile Method for the Side-Chain Protection of α-Methyl-β-3, 4-dihydroxyphenyl-L-alanine (αMeDopa) for Solid-Phase Peptide Synthesis
作者:Kun-hwa Hsieh、Margaret M. deMaine
DOI:10.1055/s-1991-26380
日期:——
Two approaches have been used to prepare N α-tert-butoxycarbonyl-α-methyl-β-3,4-dimethoxy-, or dibenzyloxyphenyl-L-alanine, N α-Boc-α-MeDopa(R)2, where R is the methyl or benzyl ether. In the first approach, α-methyl-β-3,4-dihydroxyphenyl-L-alanine (αMeDopa) is reacted with di-tert-butyl dicarbonate (Boc2O) in the presence of sodium bicarbonate under anhydrous conditions. The resultant N-protected derivative (Boc-αMeDopa) is methylated with methyl iodide/sodium carbonate, followed by reaction with methyl iodide/tetramethylammonium hydroxide, and saponification with potassium hydroxide in aqueous dioxane to give N α-tert-butoxycarbonyl-α-methyl-β-3,4-dimethoxyphenyl-L-alanine, Boc-αMeDopa(Me)2, in 30% overall yield. In the second approach, methyl ester of α-methyl-β-3,4-dihydroxyphenyl-L-alanine is prepared by the thionyl chloride/methanol procedure, followed by N-protection with di-tert-butyl dicarbonate/sodium bicarbonate, sidechain protection with benzyl chloride/tetramethylammonium hydroxide, and saponification with sodium hydroxide in aqueous dioxane to give N α-tert-butoxycarbonyl-α-methyl-β-3,4-dibenzyloxyphenyl-L-alanine, Boc-αMeDopa(CH2Ph)2, in 46% overall yield. The latter derivative has been incorporated into angiotensin II under stepwise solid-phase peptide synthesis and solution coupling conditions.
制备 N δ-叔丁氧羰基-δ-甲基-δ-3,4-二甲氧基-或二苄氧基苯基-L-丙氨酸(N δ-Boc-δ-MeDopa(R)2,其中 R 为甲基或苄基醚)的方法有两种。第一种方法是在δ-甲基-δ-3,4-二羟基苯基-L-丙氨酸(δMeDopa)与二碳酸二叔丁酯(Boc2O)在碳酸氢钠存在下于无水条件下反应。得到的 N-保护衍生物(Boc-±MeDopa)用碘甲烷/碳酸钠甲基化,然后与碘甲烷/四甲基氢氧化铵反应,并在二噁烷水溶液中用氢氧化钾皂化,得到 N δ-叔丁氧羰基-δ-甲基-δ-3,4-二甲氧基苯基-L-丙氨酸,即 Boc-δMeDopa(Me)2,总收率为 30%。 第二种方法是通过亚硫酰氯/甲醇程序制备δ-甲基-δ-3,4-二羟基苯基-L-丙氨酸甲酯,然后用二碳酸二叔丁酯/碳酸氢钠进行 N 保护、然后用二碳酸二叔丁酯/碳酸氢钠进行 N 保护,再用氯化苄/四甲基氢氧化铵进行侧链保护,最后在二噁烷水溶液中用氢氧化钠进行皂化,得到 N δ-叔丁氧羰基-δ-甲基-δ-3,4-二苄氧基苯基-L-丙氨酸,即 Boc-δ-±MeDopa(CH2Ph)2,总收率为 46%。在分步固相肽合成和溶液偶联条件下,后一种衍生物被加入到血管紧张素 II 中。