WSEAS Transactions on Biology and Biomedicine
Print ISSN: 1109-9518, E-ISSN: 2224-2902
Volume 17, 2020
A Computational Study of a Prebiotic Synthesis of the Steroid Progesterone (A and B Rings)
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Abstract: The magnesium ion metalloporphyrin complex is shown to bind the ligands propyne (p) and ethyne (e) on the metal or nitrogen pyrrole sites as a two site catalyst in their copolymerization. The order of addition of the monomers is (pepeeepee). The steroid ring D (pep) is formed first from the propyne adduct bound to the metal site and the but-diene adduct bound to the N-site. The optimal orientation of these adducts determines the β-orientation of the 17-substituent. Further reaction with hydroxyl radicals allows this to be a 17 β- acetyl substituent. Further addition of three ethyne monomers forms a N-tri-ene cyclopentene derivative able to cyclise to form the steroid ring C (pee) with a trans conformation and a 13-β methyl substituent.. Further binding of propyne on the metal site together with the N-indenyl bound adduct enables the B-ring (eep) to form with a trans orientation and a 10-β-methyl substituent. Further addition of two ethyne monomers to the Mg.porphin.N-phenanthrenyl bound adduct allows cyclisation to form the A-ring (pee). The polymerization is curtailed by reaction with hydroxyl radical to form the 3-keto substituent. The cleavage of the Mg.porphin catalyst produces the double bond of pregnane-4,5-diene-3,20-dione. The reactions have been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2 /6-31G* level, and with acceptable activation energies.
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Keywords: Prebiotic photochemical synthesis, progesterone (A & B rings), propyne, ethyne, Mg.porphin
Pages: 9-17
DOI: 10.37394/23208.2020.17.2