Title: Cucurbitacins
Literature References: A group of tetracyclic triterpenes, commonly referred to as "bitter principles of cucurbits", which have antineoplastic and anti-gibberellin activity. They are isolated from various spp of cucurbitaceous plants known since antiquity for their beneficial and toxic properties. The plants have been used as vermifuges, emetics, narcotics, and antimalarials and have been implicated in sporadic livestock poisoning in S. Africa. Seventeen cucurbitacins have been isolated, most from plants of the Cucurbitaceae family, but also from Begoniaceae, Cruciferae, Datisceae, Euphorbiaceae, and Scrophulariaceae. Cucurbitacins B and E are the most commonly identified. Isoln of cucurbitacins A, B, C, D, F: P. R. Enslin, J. Sci. Food Agric. 5, 410 (1954); of G, H, J, K, L: idem, ibid. 8, 673 (1957); of E and I: D. Lavie, S. J. Szinai, J. Am. Chem. Soc. 80, 707 (1958); of O, P, Q and antitumor activity: S. Kupchan et al., J. Org. Chem. 35, 2891 (1970). Structures of A, B, C, D, E, I: W. T. DeKock et al., J. Chem. Soc. 1963, 3828; of B, D, F: D. Lavie et al., Chem. Ind. (London) 1959, 951; of G, H: C. W. Holzapfel, P. R. Enslin, J. S. Afr. Chem. Inst. 17, 142 (1964), C.A. 62, 10467c (1965); of J, K, L: P. R. Enslin, K. B. Norton, J. Chem. Soc. 1964, 529. Stereochemistry of B, D, E, F, I: D. Lavie et al., J. Org. Chem. 28, 1790 (1963). 13C-NMR study of cucurbitacins: V. V. Velde, D. Lavie, Tetrahedron 39, 317 (1983). Use as plant growth regulators: J. Guha, S. P. Sen, Nature New Biol. 244, 273 (1973). Toxicity studies: J. LeMen et al., Chim. Ther. 4, 459 (1969); D. Albert et al., Chim. Ther. 5, 205 (1970). Reviews: D. Lavie, E. Glotter, Fortschr. Chem. Org. Naturst. 29, 308-357 (1971); J. Guha, S. P. Sen, Plant Biochem. J. 2, 12-28 (1975); A. Shrotria, Botanica 26, 28-31 (1976).
Derivative Type: Cucurbitacin B
CAS Registry Number: 6199-67-3
CAS Name: (2b,9b,10a,16a,23E)-25-(Acetyloxy)-2,16,20-trihydroxy-9-methyl-19-norlanosta-5,23-diene-3,11,22-trione
Additional Names: 1,2-dihydro-a-elaterin
Molecular Formula: C32H46O8
Molecular Weight: 558.70
Percent Composition: C 68.79%, H 8.30%, O 22.91%
Properties: Crystals from abs ethanol, mp 184-186°. [a]D25 +88° (c = 1.55 in ethanol). LD10 orally in mice: 5 mg/kg (LeMen).
Melting point: mp 184-186°
Optical Rotation: [a]D25 +88° (c = 1.55 in ethanol)
Toxicity data: LD10 orally in mice: 5 mg/kg (LeMen)
Derivative Type: Cucurbitacin E
CAS Registry Number: 18444-66-1
CAS Name: (9b,10a,16a,23E)-25-(Acetyloxy)-2,16,20-trihydroxy-9-methyl-19-norlanosta-1,5,23-triene-3,11,22-trione
Additional Names: a-elaterin
Molecular Formula: C32H44O8
Molecular Weight: 556.69
Percent Composition: C 69.04%, H 7.97%, O 22.99%
Properties: White hexagonal plates from methanol, mp 232-233° (dec). [a]D -59° (c = 0.7 in chloroform). uv max (chloroform): 234, 267 nm (e 11700, 8350). LD50 orally in mice: 340 mg/kg (Albert).
Melting point: mp 232-233° (dec)
Optical Rotation: [a]D -59° (c = 0.7 in chloroform)
Absorption maximum: uv max (chloroform): 234, 267 nm (e 11700, 8350)
Toxicity data: LD50 orally in mice: 340 mg/kg (Albert)
Cuelure Cumene Cumic Acid Cumic Alcohol Cumidine

Cucubita-5-ene with standard carbon numbering.

Cucurbitacin is any of a class of biochemical compounds that some plants — notably members of the family Cucurbitaceae, that includes the common pumpkins and gourds — developed in order to defend themselves from herbivores. Cucurbitacins are chemically classified as steroids, formally derived from cucurbitane, a triterpene hydrocarbon — specifically, from the unsaturated variant cucurbita-5-ene, or 19-(10→9β)-abeo-10α-lanost-5-ene. They often occur as glycosides.[1] They and their derivatives have been found in many plant families (including Brassicaceae, Cucurbitaceae, Scrophulariaceae, Begoniaceae, Elaeocarpaceae, Datiscaceae, Desfontainiaceae, Polemoniaceae, Primulaceae, Rubiaceae, Sterculiaceae, Rosaceae, and Thymelaeaceae), in some mushrooms (including Russula and Hebeloma) and even in some marine mollusks.

Cucurbitacins are generally cytotoxic and poisonous to some animals, and some of them are among the bitterest tastes to humans. Many have also been investigated for other biological activities.[2][3][4][5][6]