Mechanism of 1,2-hydride shift in some carbocations involved in steroid biosynthesis

Znanstveni rad - Izvorni znanstveni rad

• Autor: Valerije Vrček
• Autor: Ivana Vinković Vrček
• Autor: Olga Kronja
• Autorova ustanova: Sveučilište u Zagrebu; Farmaceutsko-biokemijski fakultet; (Zavod za organsku kemiju)
• Znanstveno / umjetničko područje, polje i grana: PRIRODNE ZNANOSTI; Kemija; Organska kemija

Sažetak (engleski)

The mechanism of 1,2-hydride shift in protosteryl C(20) cation (<b>1A</b>) and in dammarenyl C(20) cation (<b>2A</b>) was investigated by the semi-empirical AM1 method and <i>ab initio</i> quantum Chemical calculations (HF/3-21G level). Stationary points <b>1A/1B</b> and <b>2A/2B</b>, and the corresponding transition hydrido-bridged structures <b>1TS</b> and <b>2TS</b> were located on the energy surface. Process <b>1A→1B</b> turned out to be energetically more favorable than process <b>2A→2B</b> by <i>ca</i>. 9 kcal mol^-1, mostly due to the unfavorable steric repulsive interaction between the methyl group at C(14) and the <i>β</i>-oriented side chain at C(17) in <b>1A</b> and the lack of CC-hyperconjugative stabilization in <b>1A</b>. The exothermicity of processes <b>1A→1B</b> and <b>2A→2B</b> was increased by subsequent introduction of substituents (H, Me, i-Pr, and <i>t</i>-Bu) at C(14). The more pronounced trend in <b>1A→1B</b> proves that the origin of the relative stability of <b>1B</b> comes from the steric interactions in <b>1A</b>. Introduction of the halogen atom (F, Cl, and Br), due to its -I effect and relatively small size, changed the direction of the equilibrium <b>1A_Y/1B_Y</b>, and <b>1A_Y</b> was found to be by <i>ca</i>. 3 kcal mol^-1 more stable than <b>1B_Y</b>.

• Ključne riječi (engleski): steroid biosynthesis; quantum-chemical calculations; carbocations; hydride shift
• Jezik: engleski
• Vrsta publikacije: Znanstveni rad - Izvorni znanstveni rad
• Status objave: Objavljen
• Vrsta recenzije: Recenziran - međunarodna recenzija
• Verzija publikacije: Objavljena verzija rada (izdavačev PDF)
• Naslov časopisa: Croatica Chemica Acta
• Brojčani podaci: vol. 74, br. 4, str. 801-813
• p-ISSN: 0011-1643
• e-ISSN: 1334-417X
• URN:NBN: urn:nbn:hr:163:127588
• Datum objave publikacije: 2001
• URL dokumenta: https://hrcak.srce.hr/131956
• Vrsta resursa: Tekst
• Prava pristupa: Otvoreni pristup
• Datum i vrijeme pohrane: 2020-04-29 11:06:46