A Methylene Group on C-2 of 24,24-Difluoro-19-nor-1α,25-dihydroxyvitamin D₃ Markedly Increases Bone Calcium Mobilization in Vivo

Abstract

Four side chain fluorinated analogues of 1α,25-dihydroxy-19-norvitamin D have been prepared in convergent syntheses using the Wittig-Horner reaction as a key step. Structures and absolute configurations of analogues 3 and 5 were confirmed by X-ray crystallography. All analogues showed high potency in HL-60 cell differentiation and vitamin D-24-hydroxylase (24-OHase) transcription as compared to 1α,25-dihydroxyvitamin D3 (1). Most important is that all of the 20S-configured derivatives (4 and 6) had high bone mobilizing activity in vivo. However, in the 20R series, a 2-methylene group was required for high bone mobilizing activity. A change in positioning of the 20R molecule in the vitamin D receptor when the 2-methylene group is present may provide new insight into the molecular basis of bone calcium mobilization induced by vitamin D.

Synthesis of 24,24-Difluoro-1,3-<i>cis</i>-25-dihydroxy-19-norvitamin D₃ Derivatives and Evaluation of Their Vitamin D Receptor-Binding Affinity

“…14) Here we adopted similar methodology, using ketone 11 and sulfone 10. The sulfone 10 was synthesized from the Grundmann's ketone 7, which was reported by DeLuca and colleagues 13,15) (Chart 1). Compound 7 was subjected to Horner-Wittig olefination using triethyl phosphonoacetate in the presence of sodium hydride in tetrahydrofuran (THF) to give the α,β-unsaturated ester 8, and the ester was then reduced with diisobutylaluminium hydride (DIBAL)-H in toluene to give the allylic alcohol 9 in 68% yield (2 steps).…”

“…Recently, DeLuca and colleagues reported 24,24-difluoro-1α,25-(OH) 2 -19-norvitamin D 3 (4), which showed stronger vitamin D receptor (VDR) binding affinity than compound 2 and promoted bone formation more efficiently. 13) Thus, although 24-difluoro substitution has little effect on the biological potency of the natural hormone (2), it does alter the biological activity profile of 1α,25-(OH) 2 -19-norvitamin D 3 (3).…”

Design and Synthesis of Fluoro Analogues of Vitamin D

“…To our knowledge, only one report has been published on the synthesis of CD-ring fluoro-VD3 analogues. In 1994, De Clercq and coworkers designed and synthesized 11αand 11β-fluorovitamin D3 analogues (61)(62)(63)(64) with the aim of inducing a conformational change from s-trans to s-cis at the C6-C7 single bond via expected hydrogen bond formation between the C11-F and C1α-OH groups [48]. Enone (65), readily available from Grundmann's ketone, was used as a starting material.…”

“…In 1998, Iwasaki-Takayama's group reported the synthesis of (25R)-and (25S)-24,24-difluoro-1α,25,26-trihydroxyvitamin D 3 (86,87), including the X-ray crystallographic analysis of a synthetic intermediate to determine C25-stereochemistry, and proved that the 25S-isomer (87) was the main CYP24metabolite of 82 (Scheme 29B) [61]. [62]. In contrast to the previous synthetic methods starting from steroid skeletons, they demonstrated a convergent method utilizing the Wittig-Horner reaction between 24,24-difluoro-CD-rings (92,93) and a lithium salt of a phosphine oxide anion from A-ring precursors (Scheme 30).…”

“…The 20S-derivatives showed marked bone-mobilizing activity in vivo; however, 2-methylene substitution was required for such elevated activity in the 20R series. [62]. In contrast to the previous synthetic methods starting from steroid skeletons, they demonstrated a convergent method utilizing the Wittig-Horner reaction between 24,24-difluoro-CD-rings (92,93) and a lithium salt of a phosphine oxide anion from A-ring precursors (Scheme 30).…”