Cucurbitacin

It is a bitter substance found in plants of the Cucurbitaceae, Brassicaceae, Euphorbiaceae, and Bracteaceae families. A dozen or so types, A to R, are known, all of which are tetracyclic triterpenes with a rearranged lanostane skeleton. They differ in the presence or absence of desaturation (Δ ^1,2 , Δ ^23,24 ), epimerization (positions 2, 16, 21, and 24), deoxygenation (hydroxy groups at positions 2, 24, and 9), reduction (position 3), and acetylation (position 25). All are optically active, crystalline substances with melting points in the range of 140-250 °C. They exhibit ultraviolet absorption. They are soluble in organic solvents and insoluble in water. They exhibit antitumor and antigibberellin activity. Cucurbitacin E (Δ ^1,2 , Δ ^23,24 , 9-CH ₃ , 25-acetyl ester) has an LD _{50 of} 2γ/g (in mice, intravenous injection).

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

ウリ科，アブラナ科，トウダイグサ科，コマノハグサ科などの植物に含まれている苦味物質．AからRの十数種類知られているが，いずれも転位ラノスタン骨格をもつ四環性トリテルペン．それぞれは，不飽和化(Δ^1,2，Δ^23,24)，エピメリ化(2，16，21，24位)，デオキシ化(2，24位および9位のヒドロキシ基)，還元(3位)，アセチル化(25位)の有無が異なっている．いずれも光学活性で，融点140～250 ℃ の範囲に入る結晶性物質．紫外吸収を示す．有機溶媒に可溶，水に不溶．抗腫瘍活性，抗ジベレリン活性を示す．ククルビタシンE(Δ^1,2，Δ^23,24，9-CH₃，25-アセチルエステル)はLD₅₀ 2γ/g(マウス，静注)．

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