Maurits Vandewalle

Mechanisms for the selective action of Vitamin D analogs

The non-classical effects of 1,25(OH)(2)D(3) create possible therapeutic applications for immune modulation (e.g. auto-immune diseases and graft rejection), inhibition of cell proliferation (e.g. psoriasis, cancer) and induction of cell differentiation (e.g. cancer). The major drawback related to the use of 1,25(OH)(2)D(3) is its calcemic effect, which prevents the application of pharmacological concentrations. Several analogs are now available that show modest to good selectivity with regard to specific effects (e.g. anticancer or immune effects or bone anabolism versus hypercalcemia) when tested in appropriate in vivo models. The molecular basis for this selectivity is only partially understood and probably a variable mixture of mechanisms.

The Biological Activity of Nonsteroidal Vitamin D Hormone Analogs Lacking Both the C‐ and D‐Rings

1α,25‐dihydroxyvitamin D is a key calcium‐regulating hormone but also displays potent differentiating and antiproliferative activities on many cell types. The structural requirements of this secosteroid hormone have been extensively studied for the A‐ring and side chain, whereas relatively little is known about the requirements of the natural CD‐ring structure for the vitamin D–like biological activity. We have embarked on a vast program in which derivatives were synthesized and evaluated characterized by profound structural changes in the central C/D‐region. This first series of nonsteroidal analogs consists of (1R,3S)‐5‐((Z,2E)‐4‐((1S,3S)‐3‐(4‐hydroxy‐4‐methylpentyl)‐1,2,2,‐trimethylcyclopentyl)‐2‐butenylidene)‐4‐methylenecyclohexane‐1,3‐diol (KS 176) and derivatives thereof. These analogs are characterized by the absence of normal C‐ and D‐rings and by the presence of an unnatural five‐membered ring which we call the E‐ring. KS 176 with the otherwise natural side chain structure of 1α,25(OH)2D3 has between 10 and 30% of the biological activity of 1α,25(OH)2D3 when tested in vitro (prodifferentiating effects on HL‐60 and MG‐63; antiproliferating activity on MCF‐7 and keratinocytes) but has minimal in vivo calcemic effects. Introduction of several side chain modifications created analogs with increased intrinsic noncalcemic biological properties, whereas their calcemic potency remains very low. These data demonstrate that the full CD‐rings are not mandatory for the biological activity of 1α,25(OH)2D3 since they can be replaced by a new ring structure which generates an appropriate spacing of the A‐seco B‐rings in relation to the side chain. The biological activity of these nonsteroidal analogs probably involves a classical genomic activation since they are also active in transfection assays using an osteocalcin vitamin D responsive element coupled to a human growth hormone reporter gene.

Asymmetric alkylation of α-aryl substituted carbonyl compounds by means of chiral phase transfer catalysts. Applications for the synthesis of (+)-podocarp-8(14)-en-13-one and of (−)-Wy-16,225, a potent analgesic agent

Abstract Asymmetric induction in the alkylation (alkyl halides and enones) of α-aryl substituted ketones, esters and lactones by means of CPTC has been evaluated. The catalysts used are the bromides of N-(p-trifluoromethyl) benzyl derivatives of cinchonine, cinchonidine, dihydrocinchonine and dihydrocinchonidine. The potential of the method is illustrated by the asymmetric synthesis of (+)-podocarp-8(14)-ene-13-one ( 13 ) and of (−)-Wy-16,225 ( 10 ), a bridged aminotetralin with potent analgesic properties.

Biological Activity of CD‐Ring Modified 1α,25‐Dihydroxyvitamin D Analogues: C‐Ring and Five‐Membered D‐Ring Analogues

Nonsteroidal analogues of 1α,25(OH)2D3, lacking either the full five‐membered D ring (C‐ring analogues) or the full six‐membered C ring (D‐ring analogues) are more potent inhibitors of cell proliferation or inducers of cell differentiation than is 1α,25(OH)2D3. Maximal superagonistic activity was seen for the C‐ring analogue with a 24(R)‐hydroxyl group in the side chain [30‐ to 60‐fold the activity of 1α,25(OH)2D3]. The 19‐nor‐16‐ene‐26,27‐bishomo C‐ring analogue showed the best ratio of antiproliferative to calcemic effects (1275‐fold better than 1α,25(OH)2D3 and severalfold better than all vitamin D analogues so far described). The analogues are able to stimulate specific vitamin D‐dependent genes and are active in transfection assays using an osteocalcin promoter VDRE. Low binding affinity to the vitamin D binding protein, differences in metabolism, or affinity for the vitamin D receptor (VDR) are not the most important explanations for the enhanced intrinsic activity. However, the analogues are able to induce conformational changes in the VDR, which makes the VDR‐ligand complex more resistant against protease digestion than is 1α,25(OH)2D3. In contrast to 20‐epimer steroidal vitamin D analogues, 20‐epimer C‐ring analogues were less potent than analogues with a natural C‐20 configuration. In conclusion, several nonsteroidal vitamin D analogues are superagonists of 1α,25(OH)2D3 despite lower receptor affinity and, for the C‐ring analogues, higher flexibility of the side chain; moreover, they have a better selectivity profile than all analogues yet published. (J Bone Miner Res 2000;15;237–252)

Iridoids : Novel total synthesis of (±)- isoiridomyrmecin and of (±)-verbenalol

Abstract A novel synthesis of the iridoids (±)-isoiridomyrmecin 1 and (±verbenalol 2 is described starting from the tricyclo |3.3.0.02,8|octan-3-one 3 using cis fused bicyclo |3.3.0|octenes as intermediates. The heterocyclic ring of the iridoids was formed in the final stages of the syntheses.

Interaction of Two Novel 14-Epivitamin D3 Analogs with Vitamin D3 Receptor-Retinoid X Receptor Heterodimers on Vitamin D3 Responsive Elements

This study provides a detailed and exact evaluation of the interactions between vitamin D3 receptor (VDR), retinoid X receptor (RXR), and vitamin D3 responsive elements (VDREs) mediated by two novel 14‐epianalogs of 1,25‐dihydroxyvitamin D [1,25(OH)2D3], 19‐nor‐14‐epi‐23‐yne‐1,25(OH)2D3 (TX 522) and 19‐nor‐14,20‐bisepi‐23‐yne‐1,25(OH)2D3 (TX 527). Both analogs were more potent (14‐ and 75‐fold, respectively) than 1,25(OH)2D3 in inhibiting cell proliferation and inducing cell differentiation. However, DNA‐independent experiments indicated that both analogs had a lower affinity to VDR and that the stability of the induced VDR conformation, as measured by limited protease digestion assays, was similar (TX 527) or even weaker (TX 522) than that induced by the parent compound. However, DNA‐dependent assays such as gel shift experiments revealed that those analogs were slightly more potent (3–7 times) than 1,25(OH)2D3 in enhancing binding of VDR‐RXR heterodimers to a direct repeat spaced by three nucleotides (DR3) type VDRE. The functional consequences of the ligand‐VDR‐RXR‐VDRE interactions observed in vitro were subsequently evaluated in transfection experiments. Both 14‐epianalogs enhanced transcription of VDRE containing reporter constructs more efficiently than 1,25(OH)2D3 in COS‐1 and MCF‐7 cells regardless of the presence of ketoconazole. Transactivation activity is suggested to be a cell‐specific process because maximal transcriptional induction and the half‐maximal transactivation concentration for each reporter construct were different in both cell lines. The superagonistic transactivation activity closely resembled the biological potency of these analogs on the inhibition of MCF‐7 cell proliferation. These data clearly indicate that superagonistic activity starts beyond the binding of the ligand‐heterodimer (VDR‐RXR) complex to VDRE and thus probably involves coactivator/corepressor molecules.

Cyclohexane polyols : enantioselective synthesis of (+)-fortamine and of pseudosugars

Abstract (1R,2S,3R,4S)-4-butyryloxy-2,3-isopropylidenedioxy-5-cyclohexen-1-ol (1) obtained upon enzymatic hydrolysis of the corresponding meso-dibutyrate 4b is a fully functionalized homochiral building block for the synthesis of cyclohexane polyols. Applications are illustrated by the synthesis of (+)-fortamine (10) and of pseudosugars of the allo- (65,68), gulo- (35,40), manno- (54,59) and talo-series (43,48).

Synthesis, biological activity, and conformational analysis of CD-ring modified trans-decalin 1 alpha,25-dihydroxyvitamin D analogs

A novel series of analogs of 1,25-dihydroxyvitamin D3, the hormonally active metabolite of vitamin D3, characterised by the presence of a trans-fused decalin CD-ring system, possesses surprising biological activities in combination with specific structural modifications in the flexible parts of the molecule, when compared with the natural hydrindane derivatives. (1) A large difference in biological activity is observed between the 20-epimeric trans-decalin analogs that follows a pattern opposite to what is usually observed for the natural ring size. (2) Several trans-decalin analogs that are modified in the seco-B-ring region, including previtamin derivatives, possess a pronounced vitamin D-like activity, whereas the corresponding hydrindane derivatives are inactive. The molecular origin of this behavior is still under study.

A chemoenzymatic synthesis of a-ring key-intermediates for 1α,25-dihydroxyvitamin d3 and analogues

Abstract A short and practical synthesis of the 1,7-enyne A-ring intermediate and of Uskokovics phosphine-oxide precursor is described starting from the aldol product of acrolein with t-butyl acetate. Enantiopure β-hydroxy ester is obtained upon lipase-catalyzed resolution.

The synthesis of functionalized cis'-bicyclo ¦3.3.0¦octanes

Abstract A number of polyfunctionalized cis-bicycio ¦3.3.0¦octanes have been synthesized starting from the tricyclic key intermediate 5 which was obtained by the intramolecular cyclopropanation reaction of the diazo keto ester 4 . Selected stereocontrolled transformations of 5 using nucleophiles and electrophiles have been studied for the preparation of the title compounds.