Cucurbitanes

The name of about 50 naturally abundant cucurbitanes stems from Cucurbitaceae, the Latin term of cucurbitaceous plants such as cucumbers and pumpkins, known since antiquity for their beneficial and toxic properties. One of the most frequently isolated representatives is the bitter substance (+)-cucurbitacin B from Phormium tenax and Ecballium elaterium (Cucurbitaceae), also found in Iberis species (Cru-ciferae), Euphorbiaceae and Scrophulariaceae. (+)-Cucurbitacin F from Cucumis angolensis and C. dinteri is reported to inhibit the growth of human tumor cells. Toxic cucurbitacines shape the unpleasant bitter taste of salads prepared from spoiled cucumbers Cucumis sativus some representatives are reported to be antihypertonic, antirheumatic, and also active against HIV. 

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Mogroside V (2) is a cucurbitane-type triterpenoid glycoside isolated from the fhiits of Siraitia grosvenorii (Swingle) C. Jeffrey... 

The first successful transformation of a lanostane into a cucurbitane by a cationic process has been reported. On exposure to acid 3/3-acetoxy-9a-hydroxy-11-keto-5a-lanostane afforded two rearranged products (51) and (52) with a cucurbitane... 

An elegant correlation of the lanostane and cucurbitane series has been reported by Barton and his colleagues. Cucurbitacin A (46) was transformed into the cyclopropane derivative (47) by treatment of the tosylate (48) with sodium borohydride. The cyclopropane ring of the tetrahydro-compound (49) was opened by an anionic process which involved protonation of the incipient... 

Thus, once the appropriate orientation within the corresponding enzyme occurs, steroids, cucurbitacins, or other triterpenes may be formed. In the case of cucurbitacins, the squalene epoxide adopts a chair-boat-chair conformation, and the cyclization leads to a protostane cation, which is the immediate precursor of the cucurbitanes through a series of 1,2-proton and methyl group shifts, Fig. (4) [40]. 

From the anti-inflammatory, antipyretic, analgesic, and antioxidant extract of Kageneckia oblonga, Delporte et al. [13] isolated two cucurbitacins which were assayed as potential antioxidants and also as inhibitors of enzymes implicated in inflammatory reactions. Isolated compounds, 23,24-dihydrocucurbitacin F and 3P-( 3-D-glucosyloxy)-16a,23a-epoxy-cucurbitan-5,24-diene-ll-one, Fig. (11), inhibited the production of superoxide anion as well as elastase release in stimulated human neutrophils. In addition, the compounds inhibited both nitrite and... 

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