New 1α,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.

A potent analog of 1α,25-dihydroxyvitamin D 3 selectively induces bone formation

“…The introduction of a methylene group at carbon 2, removal of a methylene group at carbon 10, and alteration of the stereochemistry of the 20-carbon to yield the 20S-derivative resulted in 2-methylene-19-nor-(20S)-1␣,25(OH) 2 D 3 (2MD), a compound that exhibits an affinity for the VDR equal to that of 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] (6). This analog is highly potent in inducing human HL-60 cell differentiation in vitro, and in vivo it seems to exhibit a preferential activity on bone relative to the intestine (6). In this article, we examine the actions of 2MD on bone formation both in vitro and in vivo and contrast these actions with those of 1,25(OH) 2 D 3 .…”

Biologically active noncalcemic analogs of 1α,25-dihydroxyvitamin D with an abbreviated side chain containing no hydroxyl

“…This paper reports a series of analogs that are clearly noncalcemic but are nevertheless systemically active. Because the chromophores of these three compounds are identical, a molar extinction coefficient of 42,000 at 252 nm was used in the computation of concentration of these compounds from UV absorption data (11). The compounds were dissolved in ethyl alcohol and, with the above molar extinction coefficient, the concentrations were computed for each of them.…”

2-Methylene-19-nor-(20S)-1,25-dihydroxyvitamin D3 Potently Stimulates Gene-specific DNA Binding of the Vitamin D Receptor in Osteoblasts

“…2-Methylene-19-nor-(20S)-1,25-dihydroxyvitamin D 3 (2MD) is a highly potent 1,25(OH) 2 D 3 analog that exhibits tissueselective as well as gene-selective actions in vitro and in vivo (16,17). This compound binds to the VDR with a K d that is similar to that for 1,25(OH) 2 D 3 , although its interaction with serum vitamin D-binding protein (DBP) is exceedingly weak (Ref.…”

“…This compound binds to the VDR with a K d that is similar to that for 1,25(OH) 2 D 3 , although its interaction with serum vitamin D-binding protein (DBP) is exceedingly weak (Ref. 16). 2 In vivo studies suggest that this analog appears to localize selectively to bone relative to intestine (16).…”

“…16). 2 In vivo studies suggest that this analog appears to localize selectively to bone relative to intestine (16). 2MD strongly induces calcium resorption from bone in vivo, an activity that is likely due to its ability to induce receptor activator of NFB ligand (RANKL) from supportive stromal cells and osteoblasts.…”