title: New Synthetic Strategies to Vitamin D Analogues Modified at the Side Chain and D Ring. Synthesis of 1alpha,25-Dihydroxy-16-ene-vitamin D(3) and C-20 Analogues(1).
abstract: Two efficient synthetic routes to 1alpha,25-dihydroxy-16-ene-vitamin D(3) (4a) and their C-20 analogues (3 and 4) have been developed. Key features common to both routes A and B are the introduction of side chains functionalized at C20 (17, 21, 19, and 25). In route A the CD side chain fragments 5 and 6 are prepared by S(N)2' syn displacement of allylic carbamates 8 and 9 (X = OCONHPh) by Li(2)Cu(3)R(5). The triene unit is then constructed by assembling the latter fragments with the A-ring fragment using the Wittig-Horner method (average yield of vitamin D analogue 35%, 11-13 steps from ketone 11). In route B, the S(N)2' syn displacement of the carbamate moiety by Li(2)Cu(3)R(5) is carried out on intermediates 12 and 13, both of which bear the vitamin D triene unit (average yield of vitamin D analogue 27%, 13-15 steps from ketone 11). The latter route is particularly attractive as an approach to diverse C-20 vitamin D analogues for biological screening.
authors.affiliation: Departamento de Química Orgánica y Unidad Asociada al CSIC, Facultad de Química, Universidad de Santiago de Compostela, 15706 Santiago de Compostela, Spain.
authors.forename: María
authors.initials: M
authors.lastname: de Los Angeles Rey
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Martínez-Pérez
authors.forename: Ana
authors.initials: A
authors.lastname: Fernández-Gacio
authors.forename: Koen
authors.initials: K
authors.lastname: Halkes
authors.forename: Yagamare
authors.initials: Y
authors.lastname: Fall
authors.forename: Juan
authors.initials: J
authors.lastname: Granja
authors.forename: Antonio
authors.initials: A
authors.lastname: Mouriño