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Betulina triterpen pentacykliczny

Achrem-Achremowicz J., Janeczko Z.

Wiadomości Chemiczne

2003

[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.

Alkohol betulinowy i jego pochodne

Tomaszkiewicz-Potępa A., Piękoś M.

Wiadomości Chemiczne

2002

[Z] 56, 11-12

983-1001

Betulinic alkohol (lup-20(29)-en-3,28-diol) is a naturally occuring triterpene compound forming the principal extractive substance of the birch bark. The content of betulinol in the outer bark varies between 10-30% depending on the growth condition, age, season etc. Chemically, betulinol is a pentacyclic triterpene alcohol belonging to a lupane series of compouds. The characteristic feature of the lupane group is the five membered ring E and a-isopropyl group at C-19. Suberin and triterpenoids, the two major component groups in the outer bark of birch, have been investigated by many workers. Analytical procedures, starting with sample extraction and hydrolysis with ethanolic alkali, were developed for routine analysis, which triterpenoids to be identified by the chromatographic and spectroscopic methods. The functional groups in the betulinol molecule comprise primary and secondary hydroxyl groups and a double bond. Methods of synthesis and use of the chemical modification of betulinol has been investigated by many workers. The most investigated products from betulinol now are betulinic acid and his derivatives. It was isolated for the first time from many of plants. Betulin was convert to betulinic acid using two different synthetic routes. The first approach involved an oxidation of betulin using Jones reagent to betulonic acid and subsequent NaBH4 reduction to betulinic acid. The second approach involved steps utilizing different protecting groups on the alcohol functional groups of betulin and Jones’ oxidation to circumvent the isomerization of the secondary alcohol of betulinic acid. Betulinic acid was identified as a highly selective inhibitor of human melanoma. It has recently been reported to possess antitumor activity against cultured human melanoma cells. Betulinic acid has been modified at C-3, C-20 and C-28 positions. A series of w-undecanoic amides of betulinic acid derivatives were synthesized and evaluated for activity in human immunodeficiency virus type 1 (HIV-1). A novel series of w - aminoalkanoic acid derivatives of betulinic acid were synthesized and evaluated for their activity against human immunodeficiency virus (HIV). Effect of betulinic acid and radiotherapy on survival was demonstrated by autors.