TY - JOUR
T1 - Absolute configuration of the diterpenoids icetexone and conacytone from Salvia ballotaeflora
AU - Esquivel, Baldomero
AU - Burgueño-Tapia, Eleuterio
AU - Bustos-Brito, Celia
AU - Pérez-Hernández, Nury
AU - Quijano, Leovigildo
AU - Joseph-Nathan, Pedro
N1 - Publisher Copyright:
© 2017 Wiley Periodicals, Inc.
PY - 2018/2
Y1 - 2018/2
N2 - 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 of 1 and 3 is limited. Comparison of the substituent chemical shifts (SCS) induced by acetylation of 1 and 3 to afford 2 and 4, 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-quinone 7, on 6-hydroxythymoquinone (8) and its tautomer ortho-quinone 9, 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.
AB - 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 of 1 and 3 is limited. Comparison of the substituent chemical shifts (SCS) induced by acetylation of 1 and 3 to afford 2 and 4, 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-quinone 7, on 6-hydroxythymoquinone (8) and its tautomer ortho-quinone 9, 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.
KW - Flack parameters
KW - Hooft parameters
KW - absolute configuration
KW - hydoxy-p-benzoquinones
KW - single-crystal X-ray diffraction
KW - substituent chemical shift parameters
KW - vibrational circular dichroism
UR - http://www.scopus.com/inward/record.url?scp=85040346286&partnerID=8YFLogxK
U2 - 10.1002/chir.22781
DO - 10.1002/chir.22781
M3 - Artículo
C2 - 29110401
SN - 0899-0042
VL - 30
SP - 177
EP - 188
JO - Chirality
JF - Chirality
IS - 2
ER -