Cucurbitacin-glycosides

The transformation of the lanostane keto-epoxide (72) into the cucurbitacin derivative (73) has been achieved with boron trifluoride in acetic anhydride. The presence of the acetic anhydride appears to favour the backbone rearrangement. The structure of (73) was confirmed by correlation with the oxidation product (74) of deoxybryogenin acetate. Two new cucurbitacin glycosides, arvenins 1 (75) and II (76) from Anagallis arvensis, have been reported. ... 

Bryodulcoside (= Bryodulcosigenin glycoside) (oxygenated tetracyclic triterpene cucurbitacin glycoside) Bryonia dioica (Cucurbitaceae) [root] Sweet... 

Ubiquitous in seeds is phytic acid, the hexaphosphate ester of inositol, which has been isolated from cucurbit seeds (57). Small amounts of free sugars and terpenoid glycosides (cucurbitacins) are also present (58-60), but starch is absent (1, 1). Cellulosic cell wall materials comprise the remaining carbohydrate content. 

Finally, cucurbitacins are found in either free or glycosidic form. The form is usually linked to the presence of a hydroxyl at C-2P, C-3 and/or C-25 for monosides or at C-26 or C-27 for bidesmosides [2,3]. 

They are about 50 cucurbitacins described. They are present in plants in the form of glycosides or free aglycones. The most common of these free compounds is cucurbitacins B [3]... 

HPLC also seems to be a good method for separating cucurbitacin mixtures [3]. Since these compounds tend to exhibit at least medium polarity, an RP system is the most appropriate stationary phase (Cjg column), with a linear gradient from 20% to 50% of acetonitrile [3] or methanol [42,44] in water being the best mobile phases for separation of both free-aglycones and glycosides. In this case, previous purification of samples by means of a solid-phase extraction (SPE) is advisable. The addition of 0.01% of trifluoroacetic acid (TFA) improves the separation and reduces complications from interfering substances [3]. 

These four plants are endemic to the Mediterranean Area but have been introduced to other parts of Europe the bitter apple is also found in the savannahs of Africa. All parts of the plants are poisonous, especially roots and fruits. The compounds responsible are the cucurbitacines, a rather big family of tetracyclic triterpenes, occurring either in free form or as glycosides. They have been studied intensively (2, 43, 44, 45, 46). 

Further fractionation of the active ethanol extract of Desfontainia spinosa based on cytotoxicity has led to the discovery of two novel, cytotoxic glycosides of the parent, 11-deoxocucurbitacin I, named spinoside A (8) and spinoside B (9). The structures of 8 and 9 were established on the basis of extensive analysis of their high field NMR, NMR, high resolution mass spectra (FAB, FD, Cl, El) and chemical interconversions (ref. 57). The novel arabinopyranoside derivatives of 6 were less cytotoxic than the parent compound in the 9PS system. Cucurbitacins although highly cytotoxic have never demonstrated significant anticancer effects in vivo. 

Cueurbitacins tetracyclic triterpenes found as their glycosides in the Cucurbitaceae and Cruciferae. These toxic, bitter compounds are structurally related to the parent hydrocarbon, cucurbitane [19(10-9P)-abeo-5p-lanostane], which differs from lanostane (see Lanosterol) in the formal shift of the 10-methyl group to the 9p-position. Cucurbitacin E was formerly known as elaterin. C. have a laxative action some serve as insect attractants, and a few have antineo-plastic and antigibberellin activity. 

Cucurbitacins are the most oxygenated 30C triterpenoids with a dimethyl group at C4 and three methyl groups at C9, C13, and C14, respectively. About 50 species have been isolated and identified mainly from Cucurbitaceae species commonly in glycosides. Some of them are the most bitter substances known. Unlike common steroids, they are not methylated at C-10. Cucurbitacin D, a typical example of cucurbitacins, is a potential new therapeutic drug for treatment of T-cell leukemia. 

A special group of cucurbitacins are found in bitter melon, also known as bitter gourd or bitter squash Momordica charantia, Cucurbitaceae), which belongs to the most bitter of the edible fruits. The bitter taste of bitter melon is caused by a number of cucurbitane-type triterpenic glycosides called momordicosides, such as momordicosides K and L (8-239). Bitter melon originated in India and is now widely cultivated in Asia and Africa. The plant also contains other biologically active compounds for which it is used to treat a number of diseases, such as toothache, diarrhea, furuncle and diabetes. 

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