Görgen G, Boland W
Institut für Organische Chemie der Universität Karlsruhe, Federal Republic of Germany.
Eur J Biochem. 1989 Nov 6;185(2):237-42. doi: 10.1111/j.1432-1033.1989.tb15108.x.
Odd numbered 1-alkenes, such as 1-pentadecene or 1,8,11,14-heptadecatetraene are formed from palmitic or linolenic acid by fragmentative decarboxylation. Incubation studies with germinating safflower (Carthamus tinctorius) and (2R,3R)-12-phenyl[2,3-2H2]dodecanoic acid, (2S,3S)-12-phenyl[2,3-2H2]dodecanoic acid, (2R)-12-phenyl[2-2H]dodecanoic acid and (2S)-12-phenyl[2-2H]dodecanoic acid instead of the natural alpha-linolenic acid precursor revealed the fragmentation to be an overall anti elimination of the 3-pro(S) hydrogen and the carboxyl group (anti-periplanar transition state geometry). Externally offered 3-hydroxy acids are not fragmented to 1-alkenes. The most probable mechanistic alternatives are in agreement with abstraction of the 3-pro(S) hydrogen as a radical followed by electron transfer and fragmentation, or transient insertion of oxygen into the 3-pro(S) C-H bond and subsequent fragmentation into an 1-alkene and CO2 after appropriate activation. The mechanism seems to be of general importance for the biosynthesis of vinylic substructures of natural products from oxygenated precursors.
奇数编号的1-烯烃，如1-十五碳烯或1,8,11,14-十七碳四烯，是由棕榈酸或亚麻酸通过碎片化脱羧形成的。用发芽的红花（Carthamus tinctorius）以及（2R,3R）-12-苯基[2,3-2H₂]十二烷酸、（2S,3S）-12-苯基[2,3-2H₂]十二烷酸、（2R）-12-苯基[2-²H]十二烷酸和（2S）-12-苯基[2-²H]十二烷酸代替天然的α-亚麻酸前体进行的孵育研究表明，碎片化过程是3-pro(S)氢和羧基的总体反式消除（反式共平面过渡态几何结构）。外部提供的3-羟基酸不会碎片化生成1-烯烃。最可能的替代机制与3-pro(S)氢以自由基形式被夺取，随后进行电子转移和碎片化，或者氧瞬间插入3-pro(S) C-H键，然后在适当活化后碎片化生成1-烯烃和CO₂一致。该机制似乎对从含氧前体生物合成天然产物的乙烯基亚结构具有普遍重要性。
