Efficient synthesis of the A-ring phosphine oxide building block useful for 1 alpha,25-dihydroxy vitamin D(3) and analogues

Synthesis of a New Type of Trans-Decalin Vitamin D Analogue through a Dyotropic Ring Expansion

A new vitamin D analogue with a trans-fused decalin as the CD-ring system and containing a sulphur atom in the side chain has been synthesized in our research group. The obtention of this analogue is based on a recently discovered transformation of hydrindane cores into decalins through a dyotropic ring expansion in very mild conditions.

Isomerization of Functionalized Olefins Using the Dinuclear Catalyst [PdI(μ-Br)(PtBu3)]2: A Mechanistic Study

In a combined experimental and computational study, the isomerization activity of the dinuclear palladium(I) complex [Pd^I(μ‐Br)(P^tBu₃)]₂ towards allyl arenes, esters, amides, ethers, and alcohols has been investigated. The calculated energy profiles for catalyst activation for two alternative dinuclear and mononuclear catalytic cycles, and for catalyst deactivation are in good agreement with the experimental results. Comparison of experimentally observed E/Z ratios at incomplete conversion with calculated kinetic selectivities revealed that a substantial amount of product must form via the dinuclear pathway, in which the isomerization is promoted cooperatively by two palladium centers. The dissociation barrier towards mononuclear Pd species is relatively high, and once the catalyst enters the energetically more favorable mononuclear pathway, only a low barrier has to be overcome towards irreversible deactivation.

A more reliable synthesis of a Gemini vitamin D analog, a potentially effective chemotherapeutic agent for the treatment of colorectal carcinomas

After a serendipitous synthesis of a potentially effective chemotherapeutic agent for the treatment of colorectal carcinomas, a more reliable synthetic method is now described using our building blocks containing stereodefined stereochemistry at C-20.

A new approach to 19-nor-A-ring phosphine oxide for the convergent synthesis of 19-nor-calcitriol

A new approach to 19-nor-A-ring phosphine oxide 5 together with a convergent synthesis of the vitamin D₃ analogue 1α,25-dihydroxy-19-norvitamin D₃ (3) have been developed. The 19-nor-A-ring is constructed from (S)-carvone. The triene system is assembled by a Wittig-Horner coupling.

[3,3]-Sigmatropic rearrangement mediated synthesis of chiral building blocks for the preparation of Gemini and its analogs

[3,3]-Sigmatropic rearrangement mediated synthesis of chiral building blocks for the preparation of Gemini and its analogs.

1α,25(OH)2-3-epi-vitamin D3, a natural physiological metabolite of vitamin D3: its synthesis, biological activity and crystal structure with its receptor

Background

The 1α,25-dihydroxy-3-epi-vitamin-D₃ (1α,25(OH)₂-3-epi-D₃), a natural metabolite of the seco-steroid vitamin D₃, exerts its biological activity through binding to its cognate vitamin D nuclear receptor (VDR), a ligand dependent transcription regulator. In vivo action of 1α,25(OH)₂-3-epi-D₃ is tissue-specific and exhibits lowest calcemic effect compared to that induced by 1α,25(OH)₂D₃. To further unveil the structural mechanism and structure-activity relationships of 1α,25(OH)₂-3-epi-D₃ and its receptor complex, we characterized some of its in vitro biological properties and solved its crystal structure complexed with human VDR ligand-binding domain (LBD).

Methodology/Principal Findings

In the present study, we report the more effective synthesis with fewer steps that provides higher yield of the 3-epimer of the 1α,25(OH)₂D₃. We solved the crystal structure of its complex with the human VDR-LBD and found that this natural metabolite displays specific adaptation of the ligand-binding pocket, as the 3-epimer maintains the number of hydrogen bonds by an alternative water-mediated interaction to compensate the abolished interaction with Ser278. In addition, the biological activity of the 1α,25(OH)₂-3-epi-D₃ in primary human keratinocytes and biochemical properties are comparable to 1α,25(OH)₂D₃.

Conclusions/Significance

The physiological role of this pathway as the specific biological action of the 3-epimer remains unclear. However, its high metabolic stability together with its significant biologic activity makes this natural metabolite an interesting ligand for clinical applications. Our new findings contribute to a better understanding at molecular level how natural metabolites of 1α,25(OH)₂D₃ lead to significant activity in biological systems and we conclude that the C3-epimerization pathway produces an active metabolite with similar biochemical and biological properties to those of the 1α,25(OH)₂D₃.

Calcitriol derivatives with two different side chains at C-20. V. Potent inhibitors of mammary carcinogenesis and inducers of leukemia differentiation

Calcitriol is implicated in many cellular functions including cellular growth and differentiation, thus explaining its antitumor effects. It was shown that gemini, the calcitriol derivative containing two side chain at C20, is also active in gene transcription with enhanced antitumor activity. We have now further optimized both the A-ring and the two side chains. The chemical structures of the resulting 18 geminis were correlated with biological activities. Those containing the 1alpha-fluoro A-ring are the least active. Those featuring 23-yne and 23(E) side-chains are generally more active in human breast cancer cell growth inhibition and human leukemia cell differentiation induction than their 23(Z) counterparts. On the basis of these evaluations, we selected as lead compound a 20(R) gemini, related to calcitriol in terms of it is A-ring, where one side chain was modified by introduction of a 23-yne function and replacement of the geminal methyl groups with trifluoromethyl groups, the other created by extension of C21 with a 3-hydroxy-3-trideuteromethyl-4,4,4-trideutero-butyl moiety.

Isotope effects and the mechanism of epoxidation of cyclohexenone with tert-butyl hydroperoxide

The mechanism of the epoxidation of 2-cyclohexen-1-one with tert-butyl hydroperoxide mediated by DBU was studied by a combination of experimental kinetic isotope effects (KIEs) and theoretical calculations. A large 12C/13C (k(12C)/k(13C)) isotope effect of approximately equal to 1.032 was observed at the C3 (beta) position of cyclohexenone, while a much smaller 12C/13C isotope effect of 1.010 was observed at the C2 (alpha) position. Qualitatively, these results are indicative of nucleophilic addition to the enone being the rate-limiting step. Theoretical calculations support this interpretation. Transition structures for the addition step lead to predicted isotope effects that approximate the experimental values, while the predicted isotope effects for the ring-closure step are not consistent with the experimental values. The calculations correctly favor a rate-limiting addition step but suggest that the barriers for the addition and ring-closure steps are crudely similar in energy. The stereochemistry of these epoxidations is predicted to be governed by a preference for an initial axial addition, and the role of this preference in experimental diastereoselectivity observations is discussed.

Difluoromethyl analogs of the natural hormone 1alpha,25-dihydroxyvitamin D3: Design, synthesis, and preliminary biological evaluation

Three new Vitamin D analogs 3-5 incorporating a -CHF(2) group as an -OH surrogate have been prepared. Two of these new analogs (3 and 5) are strongly antiproliferative toward murine keratinocytes and are approximately 50 times less calciuric in vivo than the natural hormone calcitriol. The transcriptional activity of the 25-CHF(2) analog 3 is higher than that of the 1-CHF(2) analog 4.