2-Substituted-16-ene-22-thia-1alpha,25-dihydroxy-26,27-dimethyl-19-norvitamin D3 analogs: Synthesis, biological evaluation, and crystal structure.
Recently, we have found that 16-ene-22-thia-26,27-dimethyl-19-norvitamin D(3) analogs 1a (n=2, 3) are 20 times more active than the natural hormone 1alpha,25-dihydroxyvitamin D(3) in terms of transcriptional activity. To further investigate the effects of the A-ring modification of 1a, b on the biological activity profile, novel 22-thia-19-norvitamin D analogs 2-11 bearing a hydroxyethoxy-, hydroxyethylidene- or methyl group at C-2 in combination with 20S- and 20R-isomers were prepared and tested for their in vitro biological activities. All of the synthesized analogs showed 0.5-140% of the activity of the natural hormone in binding to the vitamin D receptor (VDR). When compared with the transcriptional activity of C-2 or C-20 isomeric pairs of the 22-thia analogs, the 20S-isomers 2-11a were more potent than the 20R-isomers 2, 3, 8-11b, and the 2beta-hydroxyethoxy, 2E-hydroxyethylidene, and 2alpha-methyl-2beta-hydroxy-22-thia isomers showed higher potency than their corresponding counterparts. In particular, 3a exhibited an extremely higher level of potency (210-fold) than the natural hormone. To elucidate the action mode of superagonist 3a at the molecular level, we determined the crystal structures of the rat VDR-ligand-binding domain complexed with 3a or 3b in the presence of peptide containing a nuclear box motif (LxxLL) at 1.9-2.0A resolution. The crystal structures demonstrated that the 1alpha-OH, 3beta-OH, and 25-OH groups of the natural hormone and 3a were anchored by the same amino acid residues in the ligand-binding pocket, and the terminal OH moiety of the substituent at C-2 formed hydrogen bonds with Arg270 and a water molecule to create a tight water molecule network. Moreover, the methyl groups at C-26a and C-27a make additional contact with hydrophobic residues such as Leu223, Ala227, Val230, and Ala299. These hydrophilic and hydrophobic interactions in 3a may underlie the induction of superagonistic activity.
Shimizu
Masato
M
Laboratory of Medicinal Chemistry, School of Biomedical Science, Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
Miyamoto
Yukiko
Y
Takaku
Hajime
H
Matsuo
Mayumi
M
Nakabayashi
Makoto
M
Masuno
Hiroyuki
H
Udagawa
Nobuyuki
N
DeLuca
Hector F
HF
Ikura
Teikichi
T
Ito
Nobutoshi
N
D000596:Amino Acids; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D011487:Protein Conformation; D051381:Rats; D018167:Receptors, Calcitriol / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D014867:Water / Q000737:chemistry
D000596:Amino Acids; D018167:Receptors, Calcitriol; C118756:dihydroxy-vitamin D3; D014867:Water; D014807:Vitamin D