Synthesis of 2α-Heteroarylalkyl Active Vitamin D₃ with Therapeutic Effect on Enhancing Bone Mineral Density in Vivo

Abstract

2α-Heteroarylethyl-1α,25-dihydroxyvitamin D3 analogues, which were designed to form a hydrogen bond between Arg274 of human vitamin D receptor (hVDR) and a nitrogen atom of the heteroaromatic ring at the 2α-position, were synthesized. Among them, 2α-[2-(tetrazol-2-yl)ethyl]-1α,25-dihydroxyvitamin D3 showed higher osteocalcin promoter transactivation activity in human osteosarcoma (HOS) cells and a greater therapeutic effect in ovariectomized (OVX) rats, osteoporosis model animals, on enhancing bone mineral density than those of active vitamin D3. X-ray cocrystallographic analysis of the hVDR-ligand complex confirms that the new hydrogen bond formation stabilized the complex.

Synthesis, metabolism, and biological activity of 2-[3-(tetrazolyl)propyl]-1α,25-dihydroxy-19-norvitamin D3

“…1), which showed highly potent anti-cancer activities in vitro and in vivo [7], was important for strong binding for VDR, since the corresponding compounds 2 and 4 with the tetrazole ring did not show efficient VDR binding affinity. The ethylene length between the A-ring and the tetrazole ring was also important for high binding affinity for VDR, since compound 1 showed potent VDR binding affinity and anti-osteoporosis activity in vivo [5]. As compared with the previous results of 1 [5], two methylene lengths between tetrazole and the C2 position of the A  -ring was better for biological responses through the VDR than the three methylene lengths as in 2 and 4.…”

“…Compound 6 was converted to regio-isomers 8(N2) as the major product and 8(N1) as the minor product with the tetrazolyl group through the primary alcohol 7 using the Mitsunobu reaction. The regio-isomers 8(N2) and 8(N1) were separated from each other with HPLC [isolated yields: 8(N2) in 78% and 8(N1) in 17%], and the N2-alkyl and N1-alkyl structures could be determined using a 1 H NMR method [8] and a 13 C NMR method [9] as described in the previous paper [5]. Each pivaloyl ester of 8 was reduced by DIBAL-H, and the resulting vicinal diol was treated with NaIO 4 to yield ketones 9(N2) and 9(N1), respectively (Scheme 1).…”

“…The Julia coupling reaction between 9(N1) and the CD-ring 10 proceeded smoothly to give an inseparable mixture of C2-diastereoisomers of 11 (N1) and  11 (N1) with the  O-protecting groups in 1:1.4 ratio in 89% yield [10,11], and subsequent TBAF treatment afforded deprotected [5], two methylene lengths between tetrazole and the C2 position of the A-ring was better for biological responses through the VDR than the three methylene lengths as in 2 and 4.…”

“…Previously, we reported the synthesis of and biological studies on six kinds of 2-(2-heteroarylethyl)-1 ,25(OH) (1) showed higher osteocalcin promoter transactivation activity in human osteosarcoma (HOS) cells and a greater therapeutic effect in vivo in ovariectomised (OVX) rats for enhancing bone mineral density without hypercalcemic side effects than those of the natural hormone [5]. We also found that 1 ,25  -dihydroxy-19-norvitamin D 3 derivative with the 2-(3-hydroxypropyl) group, MART-10, was an excellent VDR binder [6].…”

Synthesis and Biological Activity of 1α,2α,25-Trihydroxyvitamin D₃: Active Metabolite of 2α-(3-Hydroxypropoxy)-1α,25-dihydroxyvitamin D₃ by Human CYP3A4

“…The CD-ring bromoolefin 13 20) and enyne 12 obtained above were connected using Pd-catalyst to give the coupling product 14. 21) Desilylation by TBAF and deacetalization under acidic conditions gave the target molecule 2 22) (Chart 2).…”