Loughlin Patrick C, Willows Robert D, Chen Min
School of Biological Sciences, University of Sydney, NSW 2006, Australia.
Department of Chemistry and Biomolecular Sciences, Macquarie University, NSW 2109, Australia.
Sci Rep. 2014 Aug 14;4:6069. doi: 10.1038/srep06069.
The chemical structural differences distinguishing chlorophylls in oxygenic photosynthetic organisms are either formyl substitution (chlorophyll b, d, and f) or the degree of unsaturation (8-vinyl chlorophyll a and b) of a side chain of the macrocycle compared with chlorophyll a. We conducted an investigation of the conversion of vinyl to formyl groups among naturally occurring chlorophylls. We demonstrated the in vitro oxidative cleavage of vinyl side groups to yield formyl groups through the aid of a thiol-containing compound in aqueous reaction mixture at room temperature. Heme is required as a catalyst in aqueous solution but is not required in methanolic reaction mixture. The conversion of vinyl- to formyl- groups is independent of their position on the macrocycle, as we observed oxidative cleavages of both 3-vinyl and 8-vinyl side chains to yield formyl groups. Three new chlorophyll derivatives were synthesised using 8-vinyl chlorophyll a as substrate: 8-vinyl chlorophyll d, [8-formyl]-chlorophyll a, and [3,8-diformyl]-chlorophyll a. The structural and spectral properties will provide a signature that may aid in identification of the novel chlorophyll derivatives in natural systems. The ease of conversion of vinyl- to formyl- in chlorophylls demonstrated here has implications regarding the biosynthetic mechanism of chlorophyll d in vivo.
在产氧光合生物中，区分叶绿素的化学结构差异在于大环侧链的甲酰基取代（叶绿素b、d和f）或不饱和程度（8-乙烯基叶绿素a和b），与叶绿素a相比。我们对天然存在的叶绿素中乙烯基向甲酰基的转化进行了研究。我们证明了在室温下的水性反应混合物中，借助含硫醇的化合物，乙烯基侧链可进行体外氧化裂解以产生甲酰基。在水溶液中需要血红素作为催化剂，但在甲醇反应混合物中则不需要。乙烯基向甲酰基的转化与其在大环上的位置无关，因为我们观察到3-乙烯基和8-乙烯基侧链都发生了氧化裂解以产生甲酰基。以8-乙烯基叶绿素a为底物合成了三种新的叶绿素衍生物：8-乙烯基叶绿素d、[8-甲酰基]-叶绿素a和[3,8-二甲酰基]-叶绿素a。其结构和光谱性质将提供一种特征，可能有助于在自然系统中鉴定新型叶绿素衍生物。此处所展示的叶绿素中乙烯基向甲酰基转化的容易程度，对叶绿素d在体内的生物合成机制具有启示意义。
