Concise synthesis of 23-hydroxylated vitamin D3 metabolites

Three 23-hydroxylated vitamin D₃ derivatives, which are metabolites of 25-hydroxyvitamin D₃ produced by CYP24A1 and a related diastereomer, were efficiently synthesized. Each C23 hydroxy unit was constructed by the Claisen condensation reaction with ethyl acetate or the Grignard reaction with 2-methylallymagnesium chloride. Stereochemistry at the C23 position was determined by a modified Mosher's method. The triene structures were constructed by the Wittig-Horner reaction utilizing the A-ring phosphine oxide moiety.

Stereoselective synthesis of C24-hydroxylated vitamin D3 analogs: a practical and expeditius route to calcipotriol

The synthesis of the clinically important drug calcipotriol (2, MC903) is described as an example of a new and efficient approach to C24-hydroxylated analogs and metabolites of vitamin D3 (1). The key step of the process is the generation of the C24 stereocenter by DAIB [(-)-3-exo-(dimethylamino)isoborneol]-catalyzed addition of the alkenylzinc derivative of alkyne 3 to cyclopropylcarboxaldehyde.

Animal pharmacological effects of 24R,25-dihydroxyvitamin D3 one of the endogenous substances regulating calcium metabolism

Lewis lung carcinoma was found to cause hypercalcaemia in tumour-bearing mice. 24R,25-Dihydroxyvitamin D3, a naturally occurring steric epimer, significantly prolonged the survival time of mice with Lewis lung carcinoma. It also had an analgesic effect in mice with Lewis lung carcinoma and increased the strength of bone weakened by the carcinoma which causes abnormal calcium metabolism and results in hypercalcaemia.

Chemical synthesis of (24R)-24,25-dihydroxy[26,27-3H]vitamin D3 of high specific activity

Chemical synthesis of (24R)-24,25-dihydroxy-[26,27-3H]vitamin D3, and its 24-epimer has been devised that allows introduction of 3H at the terminal step of the synthesis. The epimeric mixture is derivatized as the tris(trimethylsilyl) ethers and resolved by high-performance liquid chromatography. The product has a specific activity of 178 Ci/mmol and is fully active in binding to the rat plasma vitamin D binding protein and in the elevation of serum calcium levels of vitamin D deficient rats. The synthesis begins with the readily available 3 beta-hydroxy-5-cholenic acid methyl ester and involves a Pummerer rearrangement, introduction of the delta 7, irradiation, and isolation of the 26,27-dinor-25-carboxylic acid methyl ester of vitamin D3. This compound is then treated with a Grignard reagent containing 3H (80 +/- 10 Ci/mmol).

Direct chemical synthesis of 1 alpha,25-dihydroxy[26,27-3H]vitamin D3 with high specific activity: its use in receptor studies

The first direct chemical synthesis of radiolabeled 1 alpha,25-dihydroxyvitamin D3 is reported. Unlike all previous syntheses, the new approach does not rely on enzymatic 1 alpha-hydroxylation of radiolabeled precursors. Rather, isotope is introduced in the last synthetic step by reaction of [3H]-methylmagnesium bromide with methyl 1 alpha-hydroxy-26,27-dinorvitamin D3-25-carboxylate to give 1 alpha,25-dihydroxy-[26,27-3H]vitamin D3 with a specific activity of 160 Ci/mmol. Mass spectroscopy confirmed that the radiohormone consists of a single isomer with six tritium atoms bound to carbons 26 and 27. Synthetically produced 1 alpha,25-dihydroxy[26,27-3H]vitamin D3 is indistinguishable from 1 alpha,25-dihydroxy-[26,27-3H]vitamin D3 obtained from the enzymatic 1 alpha-hydroxylation of 25-hydroxy[26,27-3H]vitamin D3 (160 Ci/mmol) by high-pressure liquid chromatography analysis and in the competitive binding assay using chick intestinal cytosol as the receptor source. Equilibrium dissociation constant measurements with the high specific activity radiohormone indicate a Kd of 8.2 x 10(-11) M for the chick intestinal cytosol 1 alpha,25-dihydroxyvitamin D3 receptor--a value considerably lower than the constants in the range of (1-5) x 10(-9) M previously reported.

[Synthesis of the 24 R and 24 S diastereoisomers of 24,25-dihydroxycholecalciferol (24,25(OH)2D3)]

The resolution of 5-cholestene-3 beta, 24 RS,25 triol 3,24-diacetate into the diastereoisomers 24 R and 24 S by means of liquid chromatography is described. Bromination, dehydrobromination and ultraviolet irradiation of both diastereoisomers led to 24 R,25 (OH)2D3 and 24 S,25 (OH)2D3 respectively. Their structure was further confirmed by thin layer chromatography, ultraviolet and mass spectroscopy.

Structural analogs of 1alpha,25-dihydroxycholecalciferol: preparation and biological assay of 1alpha-hydroxypregnacalciferol

The synthesis of 1alpha-hydroxypregnacalciferol, a side chain analog of 1alpha,25-dihydroxycholecalciferol (1alpha,25-dihydroxyvitamin D3), is described. Pregnenolone acetate was converted in five steps to 5-pregnen-1alpha,3beta-diol. Conversion of the diol to pregna-5,7-diene-1alpha,3beta diol diacetate followed by ultraviolet irradiation gave the corresponding previtamin derivative. Thermal isomerization, hydrolysis and chromatography then furnished the desired analog, 1alpha-hydroxypregnacalciferol. The compound was tested in vivo for its effect on intestinal calcium transport, serum calcium and phosphate levels and bone calcification, and in vitro for its effect on bone resorption. When given to intact rats, either as a single dose or in repeated daily doses, the analog even at high dose levels, exhibited no biological activity. The compound stimulated bone resorption in vitro, but only at high concentrations.

Synthesis and biological activity of 25xi,26-dihydroxycholecalciferol

25xi,26-Dihydroxycholecalciferol (25xi,26-dihydroxyvitamin D3), a metabolite of vitamin D3 preferentially active on intestine has been synthesized. This compound was prepared by converting 3beta-hydroxy-27-norcholest-5-en-25-one to 25xi,26-epoxy-5-cholesten--3beta-ol and base-catalyzed hydrolysis of the latter to 5-cholestene-3beta,25xi,26-triol; allylic bromination of the corresponding triacetate, and dehydrobromination gave the required 5,7-diene which yielded the vitamin derivative upon photolysis (Figure 3). The synthetic product shows the same activity pattern as the natural metabolite: at dose levels of 0.25 mug, the compound stimulates intestinal calcium transport, but has no effect on bone calcium mobilization in rats maintained on a vitamin D-deficient, low calcium diet. Higher doses (2.5 mug) elicit a more pronounced intestinal calcium transport response, but also have no significant effect on the bone mobilization system. The compound exhibits no biologial activity in nephrectomized animals.

Isotachysterol-3 and 25-hydroxyisotachysterol-3: analogs of 1,25-dihydrox vitamin D3

Isotachysterol(3), 25-hydroxyisotachysterol(3), and isovitamin D(3) have been synthesized and tested for biological activity. Like 1,25-dihydroxyvitamin D(3), isotachysterol(3) stimulates intestinal calcium transport and bone calcium mobilization in anephric rats, whereas 25-hydroxyvitamin D(3) does not. Although isovitamin D(3) is biologically active in normal rats it is inactive in anephric rats.