title: New 1alpha,25-dihydroxy-19-norvitamin D3 compounds of high biological activity: synthesis and biological evaluation of 2-hydroxymethyl, 2-methyl, and 2-methylene analogues.
abstract: New highly active isomers of the natural hormone 1alpha, 25-dihydroxyvitamin D3 possessing an exomethylene group at the 2-position were prepared in a convergent manner, starting with (-)-quinic acid and the corresponding (20R)- and (20S)-25-hydroxy Grundmann ketones. These 2-methylene-19-norvitamins were efficiently converted to the 2-methyl and 2-hydroxymethyl derivatives, some of which exhibited pronounced in vivo biological activity. Configurations of the A-ring substituents were determined by 1H NOE difference spectroscopy as well as by spin decoupling experiments. It was established that the bulky methyl and hydroxymethyl substituents at C-2, due to their large conformational free energies, occupy mainly equatorial positions. Additionally, hydroxylation of the C(10)-C(19) double bond in 1alpha,25-(OH)2D3 was performed, resulting in 1alpha,19,25-trihydroxy-10,19-dihydrovitamin D3 derivatives in which the hydroxymethyl substituent at C-10, for steric reasons, is forced to occupy an axial position. In consequence, the vitamin D3 analogues were synthesized in which the 1alpha-hydroxy group, required for biological activity, is almost exclusively axially or equatorially oriented because of stabilization of the single A-ring chair conformations. The relative ability of the synthesized analogues to bind the porcine intestinal vitamin D receptor was assessed and compared with that of the natural hormone. It was established that vitamins possessing the axial orientation of the 1alpha-hydroxy substituent exhibit a significantly increased receptor binding affinity. Compounds with a 2-methylene substituent showed selective calcemic activity profiles, being extremely effective on bone calcium mobilization. 2alpha-Methyl-substituted vitamins proved to be much more active in vivo than the corresponding epimers with 2beta-configuration. All of the 2-substituted vitamins exhibited pronounced HL-60 differentiating activity, those 2alpha-substituted in the 20S-series being especially potent. The present studies imply that the axial orientation of the 1alpha-hydroxy group is necessary for biological activity of vitamin D compounds.
authors.affiliation: Department of Biochemistry, College of Agricultural and Life Sciences, 420 Henry Mall, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: R R
authors.initials: RR
authors.lastname: Sicinski
authors.forename: J M
authors.initials: JM
authors.lastname: Prahl
authors.forename: C M
authors.initials: CM
authors.lastname: Smith
authors.forename: H F
authors.initials: HF
authors.lastname: DeLuca
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002136:Calcium, Dietary / Q000008:administration & dosage; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism; D008297:Male; D008968:Molecular Conformation; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism; D013329:Structure-Activity Relationship; D013552:Swine
chemical_list: D002136:Calcium, Dietary; D018167:Receptors, Calcitriol; C083610:1,25-dihydroxy-19-norvitamin D3; D002117:Calcitriol; D002118:Calcium