Analytical Sciences

Separation of Synephrine Enantiomers in Citrus Fruits by a Reversed Phase HPLC after Chiral Precolumn Derivatization

Sohei TANAKA,*1 Misaki SEKIGUCHI,*1 Atsushi YAMAMOTO,*2 Sen-ichi AIZAWA,*3 Kanta SATO,*4 Atsushi TAGA,*4 Hiroyuki TERASHIMA,*5 Yoshimi ISHIHARA,*1 and Shuji KODAMA*1

*1 School of Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
*2 Department of Biological Chemistry, College of Bioscience and Biotechnology, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan
*3 Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
*4 Department of Pharmacy, Kindai University, 3-4-1 Kowakae, Higashi-Osaka 577-8502, Japan
*5 GL Sciences Inc., 30F, Tokyo Square Tower, 6-22-1 Nishishinjuku, Shinjuku, Tokyo 163-1130, Japan

Racemic synephrine, which was transformed into diastereomers by derivatization with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosil isothiocyanate, was resolved by a reversed phase HPLC with UV detection at 254 nm. The total contents of synephrine enantiomers in citrus fruit samples were exocarp > mesocarp > endocarp > sarcocarp, suggesting that synephrine content of outer side of citrus fruits was higher than that of the inner side. (R)-Synephrine was detected in exocarp of eleven fresh citrus fruits, except for lemon, lime, and grapefruit samples. (S)-Synephrine was determined in the exocarp of four citrus fruits (mikan, orange, bitter orange, and ponkan samples) and the ratio of (S)-synephrine to total synephrine was 0.5 – 0.9%. The racemization of (R)-synephrine in aqueous solution during heating at 100°C was also examined. An increase in the heating time brought about an increase in the (S)-synephrine content in a linear fashion. The racemization was found to be significantly reduced by the addition of D-fructose, D-maltose, D-glucose, D-mannose or D-galactose, but not D-sucrose or D-mannitol. It is suggested that the reducibility of sugars may result in the inhibition of racemization.

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