Abiotic formation of uroporphyrinogen and coproporphyrinogen from acyclic reactants
作者:Jonathan S. Lindsey、Vanampally Chandrashaker、Masahiko Taniguchi、Marcin Ptaszek
DOI:10.1039/c0nj00716a
日期:——
Tetrapyrrole
macrocycles (e.g., porphyrins) have long been proposed as key ingredients in the emergence of life, yet plausible routes for forming their essential pyrrole precursor have previously not been identified. Here, the anaerobic reaction of δ-aminolevulinic acid (ALA, 5–240 mM) with 5-methoxy-3-(methoxyacetyl)levulinic acid (1-AcOH, 5–240 mM) in water (pH 5–7) at 25–85 °C for a few hours to a few days affords uroporphyrinogen, which upon chemical oxidation gives uroporphyrin in overall yield of up to 10%. The key intermediate is the α-methoxymethyl-substituted analogue of the pyrrole porphobilinogen (PBG). Reaction of ALA and the decarboxy analogue of 1-AcOH (1-Me) gave coproporphyrinogen (without its biosynthetic precursor uroporphyrinogen as an intermediate); oxidation gave the corresponding coproporphyrin in yields comparable to those for uroporphyrin. In each case a mixture of porphyrin isomers was obtained, consistent with reversible oligopyrromethane formation. The route investigated here differs from the universal extant biosynthetic pathway to tetrapyrrole macrocycles, where uroporphyrinogen (isomer III) – nature's last common precursor to corrins, heme, and chlorophylls – is derived from eight molecules of ALA (via four molecules of PBG). The demonstration of the spontaneous self-organization of eight acyclic molecules to form the porphyrinogen under simple conditions may open the door to the development of a chemical model for the prebiogenesis of tetrapyrrole macrocycles.
长期以来,四吡咯大环(如卟啉)一直被认为是生命出现的关键因素,但形成其重要吡咯前体的合理途径以前尚未发现。在这里,δ-氨基乙酰丙酸(ALA,5-240 mM)与 5-甲氧基-3-(甲氧基乙酰基)乙酰丙酸(1-AcOH,5-240 mM)在 25-85 °C 的水中(pH 5-7)经过几小时到几天的厌氧反应生成卟啉原。关键的中间体是吡咯卟啉原(PBG)的α-甲氧基甲基取代类似物。ALA 与 1-AcOH 的癸羧类似物(1-Me)反应产生共卟啉原(没有其生物合成前体尿卟啉原作为中间体);氧化产生相应的共卟啉,其产量与尿卟啉相当。在每种情况下都能得到卟啉异构体的混合物,这与低聚吡咯烷的可逆形成是一致的。这里研究的途径不同于四吡咯大环的普遍现存生物合成途径,在这种途径中,尿卟啉原(异构体 III)--自然界中卟啉、血红素和叶绿素的最后一种常见前体--来自八分子 ALA(通过四分子 PBG)。证明八个无环分子在简单条件下自发自组织形成卟啉原,可能为开发四吡咯大环的前生物生成化学模型打开了大门。