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1 Wiadomości Chemiczne

1 2003

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Betulina triterpen pentacykliczny

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Achrem-Achremowicz J. , Janeczko Z.

Wiadomości Chemiczne

2003

tom [Z] 57, 3-4

223--246

Triterpenes are the group of natural compounds widespread in the plant kingdom. They exhibit a range of biological activities. One of the most explored structures alike is betulin. This is a lupane type triterpene which is the main constituent of the extract of the white birch bark. Betulin moiety is composed of four six- and one five membered rings with one isopropenyl and two hydroxyl groups (1). Betulin and its derivatives show: antitumor , antiviral (HIV-1), antiinflammatory and antiprotosoal properties. The most promising, however, is antitumor activity. Betulinic acid - a product of the selective oxidation of betulin displays proapoptotic activity against several highly resistant tumor cells in vitro and in vivo. Apoptosis i.e. cell-suicide is induced only in "mutant" cells and not in normal ones. EC50 (effective concentration causing death of 50% of the ill cells) of betulinic acid and its derivatives lie in the pM range. Isolation, biogenesis and preparation of several modified betulin derivatives are reviewed in this article. Among the described reactions are: several routes of selective oxidation of betulin, dehydration, isomerisation, dehydrogenation, hydrogenation, glycosidation, esterification, preparation of amides (with the use of aminoacides) and synthesis of aminoderivatives. Some of these reactions give unexpected products. The biological potency of these compounds may be due to their steroid-like structures (all-trans conformation and some more similarities). The exact mechanisms of the activities, however, remain unknown. The ease of obtaining highly pure betulin and the potent biological activity of its derivatives can be the reason for singling out the compound as a lead, model triterpene for further chemical and biological investigations.