title: New convergent synthesis of 1alpha,25-dihydroxyvitamin D3 and its analogues by Suzuki-Miyaura coupling between A-ring and C,D-ring parts.
abstract: A new convergent method for the synthesis of 1alpha,25-dihydroxyvitamin D(3) and its analogues has been developed that involves efficient preparation of the A-ring part 1a, (Z)-(3S,5R)-1-bromomethylene-3,5-bis(tert-butyldimethylsilyloxy)-2-methylenecyclohexane, starting from epichlorohydrin (4) and its Suzuki-Miyaura coupling reaction with the C,D-ring part 12. Thus, (R)-4 was converted to (3S,5R)-5-(tert-butyldimethylsilyloxy)-8-(trimethylsilyl)-oct-1-en-7-yn-3-ol (3a) through a ten-step reaction sequence in 49% overall yield. Compound 3a thus obtained was treated with a Ti(O-i-Pr)(4)/2 i-PrMgCl reagent and then with NBS to afford (Z)-(1S,2S,5R)-2-bromomethyl-3-[bromo(trimethylsilyl)methylene]-5-(tert-butyldimethylsilyloxy)cyclohexanol (10a) in 51% yield, from which 1a was obtained in 87% yield by sequential treatment with TBSCl/imidazole, DBU, and Cs(2)CO(3). The resulting A-ring intermediate 1a was reacted with alkenylboronate 12 in the presence of a PdCl(2)(dppf) catalyst to furnish 1alpha,25-dihydroxyvitamin D(3) in 82% yield after protodesilylation. Similarly, all of the other three possible stereoisomers of A-ring parts 1b, 1c, and 1d were prepared, from which 1-epi-, 3-epi-, and 1,3-di-epi-1alpha,25-dihydroxyvitamin D(3) were synthesized by coupling with 12 in excellent yield, respectively. Starting from 1a and 1c, des-C,D-1alpha,25-dihydroxyvitamin D(3) analogues, retiferol 13 and its 3-epi derivative, were also prepared, respectively.
authors.affiliation: Graduate school of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hanazawa
authors.forename: Akiko
authors.initials: A
authors.lastname: Koyama
authors.forename: Kunio
authors.initials: K
authors.lastname: Nakata
authors.forename: Sentaro
authors.initials: S
authors.lastname: Okamoto
authors.forename: Fumie
authors.initials: F
authors.lastname: Sato
mesh_terms: D002117:Calcitriol / Q000031:analogs & derivatives / Q000138:chemical synthesis*; D002384:Catalysis; D003500:Cyclization; D010165:Palladium / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D010165:Palladium; D002117:Calcitriol