Absolute configuration of the diterpenoids icetexone and conacytone from Salvia ballotaeflora. Issue 2 (7th November 2017)

• Record Type: Journal Article
• Authors: Esquivel, Baldomero; Burgueño‐Tapia, Eleuterio; Bustos‐Brito, Celia; Pérez‐Hernández, Nury; Quijano, Leovigildo; Joseph‐Nathan, Pedro
• Is Part Of: Chirality. Volume 30:Issue 2(2018)
• Page Start: 177
• Page End: 188
• Publication Date: 2017-11-07
• Subjects: absolute configuration -- Flack parameters -- Hooft parameters -- hydoxy‐p‐benzoquinones -- single‐crystal X‐ray diffraction -- substituent chemical shift parameters -- vibrational circular dichroism; Chirality -- Periodicals; Pharmaceutical chemistry -- Periodicals; 541.22
• DOI: 10.1002/chir.22781
• Languages: English
• ISSNs: 0899-0042

Abstract

Abstract: Detailed literature inspections regarding the diterpenoids icetexone (1 ) and conacytone (3 ) reveal that the absolute configuration (AC) of these natural occurring compounds is not rigorously proven, despite they were originally isolated in 1976. This task is now completed by single‐crystal X‐ray diffraction Flack and Hooft parameters determination after processing data collected with Cu Kα graphite monochromated radiation. The AC of both compounds is further determined by vibrational circular dichroism measurements performed on icetexone acetate (2 ) and conacytone triacetate (4 ) since the solubility of1 and3 is limited. Comparison of the substituent chemical shifts (SCS) induced by acetylation of1 and3 to afford2 and4, respectively, reveals that in the case of icetexone, all six SCS values of the quinone ring are in excellent agreement with the expected values, while in the case of conacytone, three agree and three do not agree due to the presence of additional acetates near the quinone ring. Density functional theory calculations performed on 3‐hydroxythymoquinone (6 ) and its tautomer 4‐hydroxy‐1, 2‐quinone7, on 6‐hydroxythymoquinone (8 ) and its tautomer ortho ‐quinone9, and on icetexone (1 ) and the claimed natural occurring ortho ‐quinone tautomer romulogarzone (5 ) indicate that 2‐hydroxy‐1, 4‐quinones are more stable, by some 11‐14 kcal/mol, than their 4‐hydroxy‐1, 2‐quinone tautomers, and therefore, romulogarzone (5 ) is inexistent. Abstract :