Chemistry of Green Tea
Natural products such as green tea have attracted a great deal of attention in the last decade because of their potent anti-oxidant properties and distinct anti-cancer activity1. Catechins are important constituents of green tea and belong to the natural product class of flavonoids. The green tea flavonoids are rich in phenolic antioxidants, which are believed to be responsible for the chemoprotective potential of the tea extracts. The major polyphenolic constituents found in green tea are (-)-epicatechin, (+)-catechin, (-)-catechin, (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG) & (-)-epigallocatechin (EGC).
Chemical Structure of Catechins
Commercially prepared green tea extracts are standardized to contain 50-60% polyphenols. Recent studies have revealed that the naturally occurring polyphenolic catechins inhibit some forms of breast cancer cell proliferation2 and tumor growth and prevent recurrence of some forms of breast cancer in women3. Green tea polyphenols have also been used as chemopreventive agents for skin4, colon, pancreas, rectum5 and lung6 cancers . Recent reports also suggest that green tea may have a role to play in preventing Alzheimer's and Parkinson's diseases7. These flavonoids also possess anti-inflammatory, antiallergic, antithrombotic and antiviral properties. To date the efficacy of these flavonoids in cancer therapy is still low as compared to commercially available anticancer drugs.
However, these flavonoids provide tremendous opportunity as eco-friendly starting materials that can be chemically/enzymatically modified to yield a range of flavonoid analogues with improved efficiency.
1.“Chemoprotection: A Review of the potential therapeutic antioxidant properties of green tea (Camellia sinensis) and certain of its constituents” Mitscher, L. A.; Jung, M.; Shankel, D.; Dou, J. H.; Steele, L.; Pillai, S. P Medicinal Research Reviews, 17(4), 327, 1997.
2. “Estrogen receptor-mediated actions of polyphenolic catechins in vivo and in vitro” Goodin, M G.; Fertuck, K.C.; Zacharewski T.R.; Rosengren, R. J” Toxicological sciences, 69(2), 354, 2002.
3. Green tea polyphenols and cancer chemoprevention: multiple mechanisms and endpoints for Phase II Trials” Moyers, S. B.; Kumar, N. B. Nutrition reviews, 62(5), 204, 2004.
4. Green tea constituent (-)-epigallocatechin-3-gallate inhibits topoisomerase I activity in human colon carcinoma cells” Berger, S. J.; Gupta, S.; Belfi, C. A.; Gosky, D. M.; Mukhtar, H Biochemical and Biophysical Research Communications, 288(1), 101, 2001.
5. Green tea consumption and the risk of pancreatic and colorectal cancers” Ji, B. T.; Chow, W. H.; Hsing, A. W.; McLaughlin, J. K.; Dai. Q.; Gao, Y. T.; Blot, W. J.; Fraumeni, J. F Jr Int. J. Cancer, 70(3), 255, 1997.
6. “Cancer inhibition by green tea” Fujiki, H.; Suganuma, M.; Okabe, S.; Sueoka, N.; Komori, A.; Sueoka, E.; Kozu, T.; Tada, Y.; Suga, K.; Imai, K.; Nakachi, Kei Mutation Research, 402, 307,1998.
7. "Neurological mechanisms of green tea polyphenols in Alzheimer's and Parkinson's diseases" Weinreb, Orly; Mandel, Silvia; Amit Tamar; Youdim, Moussa B. H.Journal of Nutritional Biochemistry (2004), 15(9), 506-516.