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Resolution of isoborneol and its isomers by GC/MS to identify “synthetic” and “semi‐synthetic” borneol products
Author(s) -
Yang MingYeh,
Khine Aye Aye,
Liu JenWei,
Cheng HuiChen,
Hu Anren,
Chen HaoPing,
Shih TzengeLien
Publication year - 2018
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.23017
Subject(s) - borneol , chemistry , camphor , epimer , reagent , terpene , chromatography , stereochemistry , organic chemistry , medicine , alternative medicine , pathology , traditional chinese medicine
Borneol is a plant terpene commonly used in traditional Chinese medicine. Optically pure (+)‐borneol and (−)‐borneol can be obtained by extraction from the plants Dipterocarpaceae and Blumea balsamifera , respectively. “Synthetic borneol” is obtained from the reduction of (±)‐camphor to lead to four different stereoisomers: (+)‐isoborneol, (−)‐isoborneol, (+)‐borneol, and (−)‐borneol. In contrast, “semi‐synthetic borneol” is produced from the reduction of natural camphor, (+)‐camphor, to afford two isomers: (−)‐isoborneol and (+)‐borneol. We established a convenient method to identify them by treating the four stereoisomers with two chiral reagents, ( R )‐(+)‐α‐methoxy‐α‐trifluoromethylphenylacetyl chloride (( R )‐(+)‐MTPA‐Cl) and (1 S )‐(−)‐ camphanic chloride. The resulting derivatives from the above mentioned method were analyzed by gas chromatography. The enantiomers of (+)‐ and (−)‐isoborneol were successfully separated from (+)‐ and (−)‐borneol isomers in this study to make this a useful method in the identification of “synthetic” and “semi‐synthetic” borneols. Furthermore, we also examined five different commercial borneols. During this course, a novel and unprecedented partial epimerization from isoborneol‐camphanic ester to borneol‐camphanic ester was observed. However, this phenomenon did not occur in isoborneol‐MTPA esters epimerization to borneol‐MTPA case under the same conditions. The DFT calculation of activation energies for both reactions was in a good agreement with the results obtained from GC analysis.