Synthesis and in vitro evaluation of side chain-unsaturated analogs of 24a,24b-dihomo-1,25-dihydroxycholecalciferol

A visible-light-induced thiol addition/aerobic oxidation cascade reaction of epoxides and thiols for the synthesis of β-hydroxylsulfoxides

A photochemical thiol addition/aerobic oxidation cascade reaction has been developed. This protocol enables efficient oxidative coupling of epoxides and thiols to access structurally valuable β-hydroxylsulfoxides. A broad range of functional groups are compatible to obtain moderate to good yields of the target products. Mechanistic studies revealed a sequential reaction pathway involving base-promoted thiol addition of thiols to epoxides and visible-light-induced aerobic oxygenation of thioethers.

Differential response of lung cancer cell lines to vitamin D derivatives depending on EGFR, KRAS, p53 mutation status and VDR polymorphism

Vitamin D reveals antiproliferative activity against many types of cancer cells. Calcitriol (1,25D3), the most active form of vitamin D3, acts mainly through the vitamin D receptor, regulating the expression of target genes. Cells with reasonable expression of VDR are considered to be sensitive to antiproliferative activity of 1,25D3. However, a few alleles of the VDR gene are correlated with higher or lower response to 1,25D3 treatment. The goal of our study was to establish if cells differing in EGFR, KRAS, p53 mutation status and VDR polymorphism were sensitive to antiproliferative activity of selected vitamin D derivatives (VDDs). In our search for the lead VDD against human lung cancer cells, we selected, for this study, low calcemic analogs of active forms of vitamin D2 and D3 that had previously shown anticancer potential. The selected cell lines revealed differential response to VDDs. The highest proliferation inhibition was observed for EGFR mutant cells while a weaker response was observed for KRAS and/or p53 mutant cells. 24,24-Dihomo-1,25D3 (PRI-1890) showed the highest activity on the VDD-sensitive cell lines (A549, HCC827, NCI-H1299, and NCI-H1703). Therefore, PRI-1890 was selected as the lead VDD for further structure optimization. None of the VDDs used in this study showed antiproliferative activity against A-427 and Calu-3. VDR polymorphisms correlated inversely with sensitivity to the antiproliferative activity of VDDs since we observed less transcriptionally active form of VDR in HCC827 cells sensitive to VDD, while more transcriptionally active form was observed in NCI-H358 cells that were stimulated by VDDs to proliferate. Lack of KRAS and p53 mutations in HCC827 cells may be, therefore, responsible for the higher antiproliferative activity of VDDs, while the presence of KRAS and/or p53 mutations in other cell lines might prevent antiproliferative activity even though the VDDs were transcriptionally active as assessed on increased CYP24A1 expression. VDR gene polymorphism is not directly responsible for the sensitivity of tested cells to VDDs.

Systematic solution-phase parallel synthesis of active vitamin D3 analogs with elongated side chains and their cell differentiation activities

Side-chain elongation of active vitamin D3 is acknowledged as a structural modification to enhance its cell differentiation activity; however, the comprehensive structure-activity relationship (SAR) as a result of this modification has not been reported. To clarify the SAR, we synthesized six analogs systematically elongated at the 24-position, 26,27-position, or both by methylene (normal A-ring series 1a-f) in a facile parallel solution-phase synthesis. Using parallel synthesis, we expanded the side chain-elongation study into two 19-exomethylene analog series: 19-nor-A-ring (4a-f) and 2-methylene-19-nor-A-ring (5a-f). In the 19-nor-A-ring analog series, the SAR induced by side-chain elongation was similar to the normal A-ring analog series, but in the 2-methylene-19-nor-A-ring series, the SAR was unique.

Synthesis and antiproliferative activity of side-chain unsaturated and homologated analogs of 1,25-dihydroxyvitamin D(2). (24E)-(1S)-24-Dehydro-24a-homo-1,25-dihydroxyergocalciferol and congeners

A series of analogs of 1,25-dihydroxyergocalciferol (1-4) was synthesized and screened for their antiproliferative activity in vitro. The structure of new analogs was designed based on biological activity of the previously obtained side-chain modified analogs of vitamin D(2) and D(3). The analogs were obtained by the Julia olefination of C(22)-vitamin D sulfone 11 with side-chain aldehyde 15. The analogs were tested for their antiproliferative activity against the cells of human breast cancer lines T47D and MCF7 as well as human and mouse leukemia lines, HL-60 and WEHI-3, respectively. Analog 2 (PRI-1907) showed the strongest antiproliferative activity out of the present series of analogs of 1,25-dihydroxyvitamin D(2) with the mono homologated and double unsaturated side chain. The activity of 2 was 3-150 times stronger, depending on the cell line, than that of 1,25-dihydroxycholecalciferol (calcitriol), used as standard.

Convergent synthesis, chiral HPLC, and vitamin D receptor affinity of analogs of 1,25-dihydroxycholecalciferol

A series of analogs of 1,25-dihydroxycholecalciferol was obtained with an additional chiral center at the terminus of the aliphatic side chain (C-25). The analogs were obtained from (+)-(R)- and (-)-(S)-2-methylglycidols, by opening of the oxirane ring with the carbanions derived from vitamin D C23a,24- or C22-sulfones. The diastereomeric purity of the analogs was determined by high-performance liquid chromatography on a chiral stationary phase. The binding affinity of analogs for the calf thymus intracellular vitamin D receptor (VDR) was two orders of magnitude lower than that of the lead compound of this group, 24a,24b-dihomo-1,25-dihydroxycholecalciferol, and it was comparable to the affinity of analogs of 24-nor-1,25-dihydroxycholecalciferol. However, a twofold difference was observed for analogs diastereomeric at C-25 in their affinity for VDR. The diastereodifferentiation of the binding affinity was found to be specific for vitamin D vicinal 25,26-diols as it disappears for analogs where 26-hydroxyl, neighboring the C-25 chiral center, is replaced with methyl.

Diastereoselective synthesis, binding affinity for vitamin D receptor, and chiral stationary phase chromatography of hydroxy analogs of 1,25-dihydroxycholecalciferol and 25-hydroxycholecalciferol

A series of analogs of 1,25-dihydroxycholecalciferol and 25-hydroxycholecalciferol were obtained with an additional hydroxyl in the aliphatic side chain at carbon atom C-24. These analogs were synthesized by direct and diastereo-selective alpha-hydroxylation of enolates derived from respective vitamin D esters using Davies chiral oxaziridines. The use of (+)-(2R,8aS)-(8, 8-dichlorocamphoryl)sulfonyl oxaziridine resulted in (R) stereochemistry of the new asymmetric center for both series of analogs. Similarly, (-)-(2S,8aR) oxaziridine gave (S) analogs. The diastereomeric purity of hydroxy analogs was determined by high-performance liquid chromatography on a chiral stationary phase. High diastereopurity of hydroxylation of vitamin D esters was obtained without the use of any chiral auxiliary. The binding affinity of (24R)-1,24,25-trihydroxycholecalciferol for the calf thymus intracellular vitamin D receptor was one order of magnitude higher than that of the respective (24S)-diastereomer.

Cell differentiating and anti-proliferative activity of side-chain modified analogues of 1,25-dihydroxyvitamin D3

Besides its calcium mobilizing activity in vivo, 1,25-dihydroxyvitamin D3 has the ability to induce differentiation of human promyelocytic leukemia cells in vitro. We studied the cell differentiating activity of four novel analogues of 1,25-dihydroxyvitamin D3, using the HL60 cell line as a model. We also analyzed the influence of these compounds on the proliferation of HL60 cells, normal human keratinocytes, normal fibroblasts from human skin and human keratinocytes transfected with human papillomavirus type 16. Two of the four analogues, i.e. those with extended side-chain, were found to display similar cell differentiating and anti-proliferative activities as 1,25-dihydroxyvitamin D3. The other two analogues, with a shortened side-chain which included an additional hydroxyl, showed a substantially lower activity than that of 1,25-dihydroxyvitamin D3. We observed distinct differences in sensitivity to the anti-proliferative activity of either 1,25-dihydroxyvitamin D3 or its analogues between cells of different origin.