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Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea.
J Mass Spectrom. 2000 Jul; 35(7):860-9.JM

Abstract

Liquid chromatography/electrospray ionization mass and tandem mass spectrometry (MS/MS) techniques were used to identify two minor components and one new compound in the polyphenolic extract of green tea (Camellia sinensis). Identification and structure assignments were based on previously reported sub-structural features in the MS/MS product, precursor and neutral loss scans of reference samples. The structures of two minor components, related to the known green tea components epicatechin gallate (ECG, 5) and epigallocatechin gallate (EGCG, 6), are formed by methylation at the 3"-O-position of the gallic acid moiety. The new compound contained a gallic acid ester group, but had only one phenolic group in either the A- or B-ring, relative to the structure of 5. High-resolution mass measurements supported the empirical formula assigned to the new compounds. An important fragmentation for defining the position of methylation of the ester function involves ionization of the phenolic group at the 4"-position of the gallic acid, followed by elimination of the ester function as a neutral with concomitant formation of the m/z 169 ion. If the 4"-position is blocked by methylation, the formation of m/z 169 incorporating the gallic acid group would be blocked. Thus, the presence of an ion representing the ester group indicates a free 4"-phenol and the absence of this ion would signify the 4"-position as a site of methylation. The operation of this mechanism should be general and useful in assigning the site of methylation of any polyphenolic ester group in natural products. A similar conclusion can be drawn concerning alkylation or esterification of the 4'-position of the catechins, i. e. blocking the 4'-phenol would prevent formation of the m/z 125 ion common to all of the catechin compounds thus far examined. Therefore, mass spectral data are of considerable importance in deducing the sites of alkylation or esterification in the structures of the components of green tea.

Authors+Show Affiliations

Division of Medicinal Chemistry, College of Pharmacy, University of Arizona, Tucson 85721, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

10934439

Citation

Miketova, P, et al. "Tandem Mass Spectrometry Studies of Green Tea Catechins. Identification of Three Minor Components in the Polyphenolic Extract of Green Tea." Journal of Mass Spectrometry : JMS, vol. 35, no. 7, 2000, pp. 860-9.
Miketova P, Schram KH, Whitney J, et al. Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea. J Mass Spectrom. 2000;35(7):860-9.
Miketova, P., Schram, K. H., Whitney, J., Li, M., Huang, R., Kerns, E., Valcic, S., Timmermann, B. N., Rourick, R., & Klohr, S. (2000). Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea. Journal of Mass Spectrometry : JMS, 35(7), 860-9.
Miketova P, et al. Tandem Mass Spectrometry Studies of Green Tea Catechins. Identification of Three Minor Components in the Polyphenolic Extract of Green Tea. J Mass Spectrom. 2000;35(7):860-9. PubMed PMID: 10934439.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea. AU - Miketova,P, AU - Schram,K H, AU - Whitney,J, AU - Li,M, AU - Huang,R, AU - Kerns,E, AU - Valcic,S, AU - Timmermann,B N, AU - Rourick,R, AU - Klohr,S, PY - 2000/8/10/pubmed PY - 2000/9/9/medline PY - 2000/8/10/entrez SP - 860 EP - 9 JF - Journal of mass spectrometry : JMS JO - J Mass Spectrom VL - 35 IS - 7 N2 - Liquid chromatography/electrospray ionization mass and tandem mass spectrometry (MS/MS) techniques were used to identify two minor components and one new compound in the polyphenolic extract of green tea (Camellia sinensis). Identification and structure assignments were based on previously reported sub-structural features in the MS/MS product, precursor and neutral loss scans of reference samples. The structures of two minor components, related to the known green tea components epicatechin gallate (ECG, 5) and epigallocatechin gallate (EGCG, 6), are formed by methylation at the 3"-O-position of the gallic acid moiety. The new compound contained a gallic acid ester group, but had only one phenolic group in either the A- or B-ring, relative to the structure of 5. High-resolution mass measurements supported the empirical formula assigned to the new compounds. An important fragmentation for defining the position of methylation of the ester function involves ionization of the phenolic group at the 4"-position of the gallic acid, followed by elimination of the ester function as a neutral with concomitant formation of the m/z 169 ion. If the 4"-position is blocked by methylation, the formation of m/z 169 incorporating the gallic acid group would be blocked. Thus, the presence of an ion representing the ester group indicates a free 4"-phenol and the absence of this ion would signify the 4"-position as a site of methylation. The operation of this mechanism should be general and useful in assigning the site of methylation of any polyphenolic ester group in natural products. A similar conclusion can be drawn concerning alkylation or esterification of the 4'-position of the catechins, i. e. blocking the 4'-phenol would prevent formation of the m/z 125 ion common to all of the catechin compounds thus far examined. Therefore, mass spectral data are of considerable importance in deducing the sites of alkylation or esterification in the structures of the components of green tea. SN - 1076-5174 UR - https://www.unboundmedicine.com/medline/citation/10934439/Tandem_mass_spectrometry_studies_of_green_tea_catechins__Identification_of_three_minor_components_in_the_polyphenolic_extract_of_green_tea_ L2 - https://doi.org/10.1002/1096-9888(200007)35:7<860::AID-JMS10>3.0.CO;2-J DB - PRIME DP - Unbound Medicine ER -