The role of phospholipase C-gamma1 in 1alpha,25-dihydroxyvitamin D(3) regulated keratinocyte differentiation

Phospholipase C-gamma1 (PLC-gamma1) is the most abundant member of the phospholipase C family expressed in human keratinocytes. PLC-gamma1 is induced by 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) in normal keratinocytes via a DR6-type vitamin D responsive element. This regulation is not observed in transformed keratinocytes. The role of PLC-gamma1 in mediating 1alpha,25(OH)(2)D(3) and calcium-regulated differentiation was then tested. Both specific PLC inhibitors and antisense constructs which selectively block PLC-gamma1 production prevented 1alpha,25(OH)(2)D(3) and calcium from inducing markers of differentiation such as involucrin and transglutaminase. These studies demonstrate that PLC-gamma1 induction by 1alpha,25(OH)(2)D(3) is critical to the ability of this hormone to regulate keratinocyte differentiation.     

Antagonistic action of novel 1alpha,25-dihydroxyvitamin D3-26, 23-lactone analogs on differentiation of human leukemia cells (HL-60) induced by 1alpha,25-dihydroxyvitamin D3.

We examined the effects of two novel 1alpha,25-dihydroxyvitamin D3-26,23-lactone (1alpha,25-lactone) analogues on human promyelocytic leukemia cell (HL-60) differentiation using the evaluation system of the vitamin D nuclear receptor (VDR)/vitamin D-responsive element (DRE)-mediated genomic action stimulated by 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) and its analogues. We found that the 1alpha,25-lactone analogues (23S)-25-dehydro-1alpha-hydroxyvitamin-D3-26,23-lactone (TEI-9647), and (23R)-25-dehydro-1alpha-hydroxyvitamin-D3-26,23-lactone (TEI-9648) bound much more strongly to the VDR than the natural (23S, 25R)-1alpha,25(OH)2D3-26,23-lactone, but did not induce cell differentiation even at high concentrations (10(-6) M). Intriguingly, the differentiation of HL-60 cells induced by 1alpha,25(OH)2D3 was inhibited by either TEI-9647 or TEI-9648 but not by the natural lactone. In contrast, retinoic acid or 12-O-tetradecanoylphorbol-13-acetate-induced HL-60 cell differentiation was not blocked by TEI-9647 or TEI-9648. In separate studies, TEI-9647 (10(-7) M) was found to be an effective antagonist of both 1alpha,25(OH)2D3 (10(-8) M) mediated induction of p21(WAF1, CIP1) in HL-60 cells and activation of the luciferase reporter assay in COS-7 cells transfected with cDNA containing the DRE of the rat 25(OH)D3-24-hydroxylase gene and cDNA of the human VDR. Collectively the results strongly suggest that our novel 1alpha,25-lactone analogues, TEI-9647 and TEI-9648, are specific antagonists of 1alpha, 25(OH)2D3 action, specifically VDR/DRE-mediated genomic action. As such, they represent the first examples of antagonists, which act on the nuclear VDR.     

Biological activity of 24,24-difluoro-1 alpha, 25-dihydroxyvitamin D3 and 1 alpha, 25-dihydroxyvitamin D3-26,23-lactone in inducing differentiation of human myeloid leukemia cells

Vitamin D compounds added to the culture medium induce differentiation of human myeloid leukemia cells (HL-60 cells) by binding to a specific cytosol receptor protein. This system provides a biologically relevant and technically simple assay to examine the relationship between molecular structure and biological activity of vitamin D compounds. Using this culture system, the biological activity of 24,24-F2-1 alpha,25(OH)2D3 and 1 alpha,25(OH)2D3-26,23-lactone was assayed. 24,24-F2-1 alpha,25(OH)2D3 was four to seven times more potent than 1 alpha,25(OH)2D3 in inducing phagocytosis and C3 rosette formation of HL-60 cells, though both compounds bound equally well to the cytosol receptor, suggesting that the defuorination at the 24-carbon position may stimulate membrane permeability of the compound. 1 alpha,25(OH)2D3-26,23-lactone, on the other hand, was only 1/200th as active as 1 alpha,25(OH)2D3. The binding affinity of the lactone for the cytosol receptor was identical with that of 1 alpha (OH)D3, suggesting that the lactone formation between the 26 and 23 positions masks the function of the 25-hydroxyl group. The binding affinity of vitamin D3 derivatives to the specific cytosol receptor of HL-60 cells was well correlated with that of intestinal cytosol protein specifically bound to 1 alpha,25(OH)2D3.     

Isolation and identification of 1 alpha,25-dihydroxy-24-oxovitamin D3, 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, and 1 alpha,24(S),25-trihydroxyvitamin D3: in vivo metabolites of 1 alpha,25-dihydroxyvitamin D3

Three new in vivo metabolites of 1 alpha,25-dihydroxyvitamin D3 were isolated from the serum of dogs given large doses (two doses of 1.5 mg/dog) of 1 alpha,25-dihydroxyvitamin D3. The metabolites were isolated and purified by methanol-chloroform extraction and a series of chromatographic procedures. By cochromatography on a high-performance liquid chromatograph, ultraviolet absorption spectrophotometry, mass spectrometry, Fourier-transform infrared spectrophotometry, and specific chemical reactions, the metabolites were identified as 1 alpha,25-dihydroxy-24- oxovitamin D3, 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, and 1 alpha,24(S),25-trihydroxyvitamin D3. According to these procedures, the total amounts of the isolated metabolites were as follows: 1 alpha,25-dihydroxyvitamin D3, 23.6 micrograms; 1 alpha,25-dihydroxy-24- oxovitamin D3, 1.8 micrograms; 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, 9.2 micrograms; 1 alpha,24(R),25-trihydroxyvitamin D3, 15.4 micrograms; 1 alpha,24(S),25-trihydroxyvitamin D3, 1.0 microgram. With recovery corrections, the serum levels of each metabolite were approximately 49 ng/mL for 1 alpha,25-dihydroxyvitamin D3, 3.7 ng/mL for 1 alpha,25-dihydroxy-24- oxovitamin D3, 19 ng/mL for 1 alpha,25-dihydroxyvitamin D3 26,23-lactone, 32 ng/mL for 1 alpha,24(R),25-trihydroxyvitamin D3, and 2.1 ng/mL for 1 alpha,24(S),25-trihydroxyvitamin D3.     

1 alpha-hydroxy-25-fluorovitamin D3: a potent analogue of 1 alpha,25-dihydroxyvitamin D3

Chemically synthesized 1 alpha-hydroxy-25-fluorovitamin D3 was compared to 1,25-dihydroxyvitamin D3 for potency in the chick intestinal cytosol-binding protein assay, induction of intestinal calcium transport, mobilization of calcium from bone, and epiphyseal plate calcification in the rat. The 25-fluorinated analogue causes 50% displacement of 1,25-dihydroxy[23,24-3H]D3 at 1.8 X 10(-8) M in the competitive protein-binding assay, whereas only 5.6 X 10(-11) M of unlabeled 1,25-dihydroxyvitamin D3 is needed for equal competition. This 315-fold difference between and 1 alpha-hydroxy-25-fluorovitamin D3 indicates that the fluoro analogue is about equipotent with 1 alpha-hydroxyvitamin D3 in the protein-binding assay. However, 1 alpha-hydroxy-25-fluorovitamin D3 is 1/50 as active as 1,25-dihydroxyvitamin D3 in vivo in the stimulation of intestinal calcium transport and bone calcium mobilization in vitamin D deficient rats on a low-calcium diet. Likewise, 1 alpha-hydroxy-25-fluorovitamin D3 is about 40 times less active than 1,25-dihydroxyvitamin D3 in inducing endochondrial calcification in rachitic rats. No selective actions of 1alpha-hydroxy-25-fluorovitamin D3 were noted. Since the 25 position of the analogue is blocked by a fluorine atom, it appears that 25-hydroxylation of 1 alpha-hydroxylated vitamin D compounds in vivo is not an obligatory requirement for appreciable vitamin D activity.     

The role of Ca2+ and protein kinase C in the differentiation of HL-60 cells induced by 1 alpha,25(OH)2D3 and diltiazem

The roles of calcium (Ca2+) and protein kinase C in the differentiation of HL-60 cells induced by 1 alpha,25(OH)2D3 (D3) and/or a Ca2+ antagonist, diltiazem(D-cis, L-cis), were elucidated. D3 and diltiazem (100 microM) inhibited cell proliferation, and diltiazem enhanced the D3-induced differentiation. There was no difference in potency between the two isomers of diltiazem in the enhancing activity, in spite of their different pharmacological activity. The concentration of free Ca2+ in the HL-60 cells following D3 and/or diltiazem treatment significantly increased. A protein kinase C inhibitor, H-7, inhibited the phenotypic differentiation induced by D3. These results suggest that Ca2+ and protein kinase C play an important role in the differentiation of HL-60 cells induced by D3 and diltiazem.     

Inhibition by 1 alpha,25-dihydroxyvitamin D3 of dimethyl sulfoxide-induced differentiation of Friend erythroleukemia cells

Regulation of erythroid differentiation by vitamin D3 derivatives was examined in Friend erythroleukemia cells. After Friend cells were cultured for 5 days with 1.5% dimethyl sulfoxide (DMSO), as much as 70% of the cells became benzidine-positive and the hemoglobin content increased in parallel with the increase of benzidine-positive cells. The DMSO-induced erythroid differentiation was markedly inhibited by concurrent addition of the active form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3]. Of the vitamin D3 derivatives tested, 1 alpha,25(OH)2D3 was the most potent in inhibiting DMSO-induced erythroid differentiation. 1 alpha,25(OH)2D3 alone was totally ineffective in both cell growth and erythroid differentiation. These results together with our previous reports indicate that 1 alpha,25(OH)2D3 is somehow involved not only in myeloid differentiation, but also in erythroid differentiation.     

Regulation of human pulmonary surfactant protein gene expression by 1alpha,25-dihydroxyvitamin D3

1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] has been reported to stimulate lung maturity, alveolar type II cell differentiation, and pulmonary surfactant synthesis in rat lung. We hypothesized that 1,25(OH)(2)D(3) stimulates expression of surfactant protein-A (SP-A), SP-B, and SP-C in human fetal lung and type II cells. We found that immunoreactive vitamin D receptor was detectable in fetal lung tissue and type II cells only when incubated with 1,25(OH)(2)D(3). 1,25(OH)(2)D(3) significantly decreased SP-A mRNA in human fetal lung tissue but did not significantly decrease SP-A protein in the tissue. In type II cells, 1,25(OH)(2)D(3) alone had no significant effect on SP-A mRNA or protein levels but reduced SP-A mRNA and protein in a dose-dependent manner when the cells were incubated with cAMP. SP-A mRNA levels in NCI-H441 cells, a nonciliated bronchiolar epithelial (Clara) cell line, were decreased in a dose-dependent manner in the absence or presence of cAMP. 1,25(OH)(2)D(3) had no significant effect on SP-B mRNA levels in lung tissue but increased SP-B mRNA and protein levels in type II cells incubated in the absence or presence of cAMP. Expression of SP-C mRNA was unaffected by 1,25(OH)(2)D(3) in lung tissue incubated +/- cAMP. These results suggest that regulation of surfactant protein gene expression in human lung and type II cells by 1,25(OH)(2)D(3) is not coordinated; 1,25(OH)(2)D(3) decreases SP-A mRNA and protein levels in both fetal lung tissue and type II cells, increases SP-B mRNA and protein levels only in type II cells, and has no effect on SP-C mRNA levels.     

Calvarial cells synthesize 1 alpha,25-dihydroxyvitamin D3 from 25-hydroxyvitamin D3

A metabolite of vitamin D has been isolated in pure form from incubation of 25-hydroxyvitamin D3 with embryonic chick calvarial cells that had been grown on Cytodex 1 microcarrier beads. The isolation involved dichloromethane extraction of the cells and incubation medium, followed by Sephadex LH-20 column chromatography and high-performance liquid chromatography of the extract. The metabolite was identified as 1 alpha,25-dihydroxyvitamin D3 by means of ultraviolet absorption spectroscopy, mass spectrometry, and sensitivity to oxidation by periodate. This metabolite was not produced by cell-free medium or by cells from embryonic chick liver, skin, or heart. In conclusion, (1) kidney cells are not unique in having 25-hydroxyvitamin D3:1 alpha-hydroxylase activity as previously believed and (2) vitamin D target tissues such as the skeleton may play a direct role in mediating the metabolism of 25-hydroxyvitamin D3 to 1 alpha,25-dihydroxyvitamin D3, a vitamin D metabolite active at those sites.     

Biological activity of 1 alpha, 25-dihydroxyvitamin D derivatives--24-epi-1 alpha, 25-dihydroxyvitamin D-2 and 1 alpha,25-dihydroxyvitamin D-7

Biological activity of 24-epi-1 alpha,25-dihydroxyvitamin D-2 (24-epi-1,25(OH)2D2) and 1 alpha,25-dihydroxyvitamin D-7 (1,25(OH)2D7), the 22,23-dihydro derivative of the former compound, was investigated. Both of the vitamin D derivatives stimulated intestinal calcium transport and calcium mobilization from bones in rats; however, the effect was about 50% of that of 1 alpha,25-dihydroxyvitamin D-3 (1,25(OH)2D3). On the other hand, 24-epi-1,25(OH)2D2 and 1,25(OH)2D7 inducement of HL-60 human leukemia cell differentiation was comparable to that of 1,25(OH)2D3. Accordingly, the differentiation-inducing activity of 24-epi-1,25(OH)2D2 and 1,25(OH)2D7 was much greater than their ability to stimulate calcium metabolism. In contrast to 1,25(OH)2D3, 24-epi-1,25(OH)2D2 and 1,25(OH)2D7 exerted little hypercalcemic activity in mice. These results suggest that both vitamin D derivatives will be useful as anti-tumor agents.     

Role of protein kinase C alpha in calcium induced keratinocyte differentiation: defective regulation in squamous cell carcinoma

Calcium induces both involucrin and transglutaminase-K in normal keratinocytes (NHK) but not in squamous carcinoma cell lines (SCC). The protein kinase C (PKC) agonist phorbol myristoyl acetate potentiates and the PKC antagonist Ro31-8220 blocks the ability of calcium to stimulate the involucrin promoter in normal human keratinocytes but not in SCC4. We thus examined the ability of calcium to regulate the levels of five PKC isozymes in NHK and two SCC. In the normal keratinocytes, the levels of PKC [alpha], PKC [delta], PKC [eta], and PKC [zeta] increased over the first one to two weeks in a calcium-and time-dependent manner. PKC [epsilon] decreased in a time-and calcium-dependent fashion over the three-week period. All five isozymes showed little change during culture in SCC4 at any calcium concentration. Calcium and time of culture had partial effects on SCC12B2, a carcinoma that shows partial differentiation characteristics. Since PKC [alpha] is the only calcium responsive PKC isozyme in keratinocytes and most likely to be directly involved in calcium induced differentiation, we evaluated the effect of inhibiting its production with antisense oligonucleotides on calcium-regulated markers of differentiation. We found that the PKC [alpha] specific antisense oligonucleotide blocked calcium stimulated involucrin promoter activity as well as PKC [alpha], involucrin, and transglutaminase protein production, whereas the sense oligonucleotide control did not. We conclude that although a number of PKC isozymes are regulated during calcium-induced differentiation, PKC [alpha] plays a necessary role in mediating calcium-induced differentiation. Failure to regulate PKC [alpha] in SCC4 may underlie at least part of the failure of calcium to promote differentiation in these cells.     

Calcium is essential in the fusion of mouse alveolar macrophages induced by 1 alpha,25-dihydroxyvitamin D3

We have reported that the active form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3], directly induces activation and fusion of mouse alveolar macrophages (Abe et al., 1983, 1984). The activated state appeared to be a prerequisite to the fusion of macrophages. Macrophages began to fuse 36 hr after adding 1 alpha,25(OH)2D3; the fusion rate attained a maximum of 70-80% at 72 hr. During the course of further investigating the mechanisms of fusion induced by the vitamin, we found that the calcium ion is closely involved in the fusion process of macrophages induced by 1 alpha,25(OH)2D3. When alveolar macrophages were cultured with 1 alpha,25(OH)2D3 in medium with graded concentrations (0.13-1.85 mM) of calcium, the fusion rate went down in parallel with the decrease of medium calcium. Neither calcium ionophore A23187 nor 12-O-tetradecanoylphorbol-13-acetate (TPA) induced fusion of freshly isolated macrophages, but the two compounds greatly promoted fusion of the macrophages pretreated for 18 hr with 1 alpha,25(OH)2D3. The vitamin effect for the first 18 hr was similar, irrespective of the medium calcium concentration. In contrast, millimolar amounts of calcium were essential in the subsequent period of incubation(18-72 hr) for inducing fusion. The activation of macrophages measured by the induction of cytotoxicity and the enhancement of glucose consumption by 1 alpha,25(OH)2D3 occurred similarly, irrespective of the medium calcium concentration. These results clearly indicate that the fusion process of alveolar macrophages induced by 1 alpha,25(OH)2D3 can be divided into two phases: 1) the calcium-independent priming phase (0-18 hr) and 2) the calcium-dependent progression phase (18-72 hr). 1 alpha,25(OH)2D3 is necessary only in the priming phase; A23187 and TPA can be substituted for 1 alpha,25(OH)2D3 in the progression phase.     

Production in vitro of 1 alpha,25-dihydroxyvitamin D3-26,23-lactone from 1 alpha,25-dihydroxyvitamin D2 by rat small intestinal mucosa homogenates

The metabolism of 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃] in the rat has been studied under both in vivo and in vitro conditions. A time course study of the appearance of 1α,25-dihydroxyvitamin D₃-26,23-lactone in the plasma following intravenous or oral administration of 1α,25(OH)₂D₃ suggests that the small intestine may take part in production of the 1α,25(OH)₂D₃-26,23-lactone. In an in vitro study using a homogenate of rat small intestinal mucosa, 1α,25(OH)₂D₃ undergoes further metabolism to give more polar metabolite(s) which comigrate with authentic 1α,24,25-trihydroxyvitamin D₃ [1α,24,25(OH)₃D₃] on Sephadex LH-20 column chromatography. The metabolic profile obtained after high-pressure liquid chromatography reveals two major classes of metabolites, designated Peaks X and Y. Peak X is an unidentified metabolite of 1α,25(OH)₂D₃. Peak Y is chromatographically identical with 1α,25-dihydroxyvitamin D₃-26,23-lactone which has been recently isolated from the plasma of rats and dogs as a major metabolite produced in vivo from either 1α,25(OH)₂D₃ or 1α-hydroxyvitamin D₃ (N. Ohnuma, K. Bannai, H. Yamaguchi, Y. Hashimoto, and A. W. Norman, 1980, Arch. Biochem. Biophys.204, 387). The enzyme activity which produces metabolites X and Y in the rat intestinal homogenates is induced in vitamin D-replete rats by pretreatment of the animals with intravenous 1.25 μg/kg doses of 1α,25-dihydroxyvitamin D₃, 6 to 8 h previously.     

2,2-Functionalized analogues of 1alpha,25-dihydroxyvitamin D3, the potent inducers of cell differentiation

All four possible A-ring stereoisomers of 2,2-dimethyl-1,25-dihydroxyvitamin D(3) (4) were designed and convergently synthesized. Nine-step conversion of methyl hydroxypivalate 6 provided the desired A-ring enyne synthon (13a,b) in good overall yield. Cross-coupling reaction of the A-ring synthon 13a,b with the CD-ring portion in the presence of palladium catalyst, followed by deprotection, gave the vitamin analogues (4a-d). We also synthesized four stereoisomers of 2,2-ethano-1,25-dihydroxyvitamin D(3) (5), as novel spiro-ring analogues having cyclopropane fused at the C2 position. Biological potencies of the synthesized compounds were assessed in terms of the vitamin D receptor (VDR) binding affinity, as well as the HL-60 cell differentiation-inducing activity. The 2,2-ethano analogue 5a showed a comparable activity to the natural hormone 1, while the 2,2-dimethyl analogue 4a exhibited one-third of the activity of 1 in cell differentiation, with the reduced VDR binding affinity.     

The antagonism between 2-methyl-1,25-dihydroxyvitamin D3 and 2-methyl-20-epi-1,25-dihydroxyvitamin D3 in non-genomic pathway-mediated biological responses induced by 1alpha,25-dihydroxyvitamin D3 assessed by NB4 cell differentiation

We synthesized all eight possible A-ring diastereomers of 2-methyl substituted analogs of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and also all eight A-ring diastereomers of 2-methyl-20-epi-1alpha,25(OH)2D3. Their biological activities, especially the antagonistic effect on non-genomic pathway-mediated responses induced by 1alpha,25(OH)2D3 or its 6-s-cis-conformer analog, 1alpha,25(OH)2-lumisterol3, were assessed using an NB4 cell differentiation system. Antagonistic activity was observed for the 1beta-hydroxyl diastereomers, including 2beta-methyl-1beta,25(OH)2D3 and 2beta-methyl-3-epi-1beta,25(OH)2D3. Very interestingly, 2beta-methyl-3-epi-1alpha,25(OH)2D3 also antagonized the non-genomic pathway, despite its 1alpha-hydroxyl group. Other 1alpha-hydroxyl diastereomers did not show antagonistic activity. 20-epimerization diminished the antagonistic effect of all of these analogs on the non-genomic pathway. These findings suggested that the combination of the 2-methyl substitution of the A-ring and 20-epimerization of the side chain could alter the biological activities in terms of antagonism of non-genomic pathway-mediated biological response. Based on a previous report, 2-methyl substitution alters the equilibrium of the A-ring conformation between the alpha- and beta-chair conformers. The 2beta-methyl diastereomers, which exhibited antagonism on non-genomic pathway-mediated response, were considered to prefer the beta-conformer. Further examination to elucidate the relationship between the altered ligand shape and receptors interaction will be important for molecular level understanding of the mechanism of antagonism of the non-genomic pathway.     

Metabolic pathways from 1 alpha,25-dihydroxyvitamin D3 to 1 alpha,25-dihydroxyvitamin D3-26,23-lactone. Stereo-retained and stereo-selective lactonization

The present study was carried out in order to elucidate the metabolic pathway from 1 alpha,25-(OH)2D3 to 1 alpha,25-(OH)2D3-26,23-lactone. For that purpose, we stereospecifically synthesized the vitamin D3 derivatives 1 alpha,23(S),25-(OH)3D3, 1 alpha,23(S),25(R),26-tetrahydroxyvitamin D3, and 23(S),25(R)-1 alpha,25-dihydroxyvitamin D3-lactol. The in vitro metabolism of these compounds was examined in kidney homogenates and intestinal mucosa homogenates from 1 alpha,25-(OH)2D3-supplemented chicks. The naturally occurring 23(S),25(R)-1 alpha,25-dihydroxyvitamin D3-26,23-lactone was produced (in increasing amounts) from 1 alpha,25-(OH)2D3, 1 alpha,25(R),26-(OH)3D3, 1 alpha,23(S),25-(OH),D3, 1 alpha,23(S),25(R),26-(OH)4D3, and 23(S),25(R)-1 alpha,25-(OH)2D3-26,23-lactol. These results indicated that there are two possible metabolic pathways from 1 alpha,25-(OH)2D3 to 1 alpha,23(S),25(R),26-(OH)4D3: the major one is by way of 1 alpha,23(S),25-(OH)3D3 and the minor one is by way of 1 alpha,25(R),26-(OH)3D3. 1 alpha,23(S),25(R),26-Tetrahydroxyvitamin D3 is further metabolized to 23(S),25(R)-1 alpha,25-dihydroxyvitamin D3-26,23-lactone via 23(S),25(R)-1 alpha,25-dihydroxyvitamin D3-26,23-lactol. In the course of our studies, a new biosynthetic vitamin D3 metabolite was isolated in pure form. This metabolite was identified as 23(S),25(R)-1 alpha,25-(OH)2D3-26,23-lactol by UV spectrophotometry and mass spectrometry. Furthermore, we establish in this report that the lactonization of 1 alpha,23,25,26-(OH)4D3 and 1 alpha,25-(OH)2D3-26,23-lactol occurs in a stereo-retained and stereo-selective fashion.     

Synthesis of 1alpha,25-dihydroxyvitamin D3-26,23-lactams (DLAMs), a novel series of 1 alpha,25-dihydroxyvitamin D3 antagonist

Novel vitamin D(3) analogs having a lactam structure in their side chains, 1 alpha,25-dihydroxyvitamin D(3)-26,23-lactams (DLAMs), were designed based on the principle of regulation of the folding of helix-12 in the vitamin D nuclear receptor (VDR). The new analogs were synthesized via 1,3-dipolar cycloaddition reaction and subsequent reduction of the isoxazolidine as key steps. Among the analogs, (23S,25S)-DLAM-01 (4a) and (23S,25S)-DLAM-1P (5a) bind strongly to VDR. Moreover, these analogs were found to inhibit the differentiation of HL-60 cells induced by 1 alpha,25-dihydroxyvitamin D(3).