Thompson M J, Meudt W J, Mandava N B, Dutky S R, Lusby W R, Spaulding D W
Steroids. 1982 Jan;39(1):89-105. doi: 10.1016/0039-128x(82)90129-5.
A number of brassinosteroids with and without hydroxyl groups or an alkyl substituent in their side chain were synthesized. The alkyl substituent at C-24 highly influenced the oxidation of the C-22 double bond with osmium tetroxide and, hence the ratio of the 22 beta,23 beta- and 22 alpha,23 alpha-glycolic isomers obtained. Two different bean bioassays used to compare the plant growth-promoting capabilities of these compounds and of brassinolide and its three side chain 22,23-cis-glycolic isomers showed that brassinolide was the most active. The next most active brassinosteroids were generally those with 22 alpha-OH, 23 alpha-OH orientation and a beta-methyl or alpha-ethyl substituent at C-24. Similarly, of the synthetic precursor tetrahydroxy ketones of the brassinosteroids, those with 22 alpha-OH, 23 alpha-OH orientation (like brassinolide) and an alkyl group at C-24 were also the most active in both bioassays. The results indicate stringent structural features are required for a steroid to induce brassin activity. The structural requirements are: a trans A/B ring system (5alpha-hydrogen), a 6-ketone or a 7-oxa-6-ketone system in ring B, cis alpha-oriented hydroxyl groups at C-2 and C-3, cis hydroxy groups at C-22 and C-23 as well as a methyl or ethyl substituent at C-24.
合成了多种在其侧链带有或不带有羟基或烷基取代基的油菜素甾体。C-24位的烷基取代基对四氧化锇氧化C-22双键有很大影响，因此也影响了所得到的22β,23β-二醇异构体和22α,23α-二醇异构体的比例。两种不同的菜豆生物测定法被用于比较这些化合物以及油菜素内酯及其三种侧链22,23-顺式二醇异构体促进植物生长的能力，结果表明油菜素内酯活性最高。接下来活性最高的油菜素甾体通常是那些具有22α-OH、23α-OH取向且在C-24位带有β-甲基或α-乙基取代基的化合物。同样，在油菜素甾体的合成前体四羟基酮中，那些具有22α-OH、23α-OH取向（如油菜素内酯）且在C-24位带有烷基的化合物在这两种生物测定中也最具活性。结果表明，甾体诱导油菜素活性需要严格的结构特征。结构要求为：反式A/B环系（5α-氢）、B环中的6-酮或7-氧杂-6-酮体系、C-2和C-3位的顺式α-取向羟基、C-22和C-23位的顺式羟基以及C-24位的甲基或乙基取代基。
