title: Synthesis of brassinosteroids with a keto group in the side chain.
abstract: The aim of this work was to prepare 24-epicryptolide and 22-dehydro-24-epibrassinolide as possible metabolites of 24-epibrassinolide. The main synthetic problem to be solved was the differentiation of functional groups in brassinosteroids. Distinguishing 2α,3α-diol function from another diol group in 24-epibrassinolide was achieved via selective hydrolysis of 2α,3α-cyclic carbonate or via regioselective reaction of boric acid with the functional groups in the side chain. The hydroxyl at C-23 was more reactive than the 22-OH in the oxidation with bromine in the presence of bis(tributyltin) oxide and in the benzylation reaction that resulted in the predominant formation of the corresponding α-hydroxy ketone derivatives with the ratio ranging from 4:1 to 1.5:1.
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str., 5/2, 220141 Minsk, Belarus.
authors.forename: Aliona G
authors.initials: AG
authors.lastname: Baradzenka
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str., 5/2, 220141 Minsk, Belarus.
authors.forename: Barys M
authors.initials: BM
authors.lastname: Barysau
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str., 5/2, 220141 Minsk, Belarus.
authors.forename: Alaksiej L
authors.initials: AL
authors.lastname: Hurski
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str., 5/2, 220141 Minsk, Belarus. Electronic address: vz@iboch.bas-net.by.
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Zhabinskii
authors.affiliation: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich Str., 5/2, 220141 Minsk, Belarus.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Khripach
mesh_terms: D001888:Boric Acids / Q000737:chemistry; D060406:Brassinosteroids / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D006868:Hydrolysis; D007659:Ketones / Q000737:chemistry*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013256:Steroids / Q000138:chemical synthesis* / Q000737:chemistry*; D013260:Steroids, Heterocyclic / Q000737:chemistry*
chemical_list: D001888:Boric Acids; D060406:Brassinosteroids; D007659:Ketones; D013256:Steroids; D013260:Steroids, Heterocyclic; C032688:boric acid; C023623:brassinolide
keywords: 22-Dehydro-24-epibrassinolide; 24-Epibrassinolide; 24-Epicryptolide; Boric acid ester; Brassinosteroids