Design, synthesis, and biological activity of D-bishomo-1α,25-dihydroxyvitamin D analogs and their crystal structures with the vitamin D nuclear receptor.

The biologically active metabolite of vitamin D - calcitriol - is a hormone involved in the regulation of calcium-phosphate homeostasis, immunological processes and cell differentiation, being therefore essential for the proper functioning of the human body. This suggests many applications of this steroid in the treatment of diseases such as rickets, psoriasis and some cancers. Unfortunately, using therapeutic doses of calcitriol is associated with high concentrations of this compound which causes hypercalcemia.

Chemical synthesis, biological activities and action on nuclear receptors of 20S(OH)D, 20S,25(OH)D, 20S,23S(OH)D and 20S,23R(OH)D.

New and more efficient routes of chemical synthesis of vitamin D (D) hydroxy (OH) metabolites, including 20S(OH)D, 20S,23S(OH)D and 20S,25(OH)D, that are endogenously produced in the human body by CYP11A1, and of 20S,23R(OH)D were established. The biological evaluation showed that these compounds exhibited similar properties to each other regarding inhibition of cell proliferation and induction of cell differentiation but with subtle and quantitative differences. They showed both overlapping and differential effects on T-cell immune activity.

Novel superagonist analogs of 2-methylene calcitriol: Design, molecular docking, synthesis and biological evaluation.

A new series of highly biologically active (20S,22R)-1α,25-dihydroxy-22-methyl-2-methylene-vitamin D analogs, possessing different side chains, have been efficiently prepared as potential agents for medical therapy. Design of these synthetic targets was based on the analysis of the literature data and molecular docking experiments. The synthetic strategy involved Sonogashira coupling of the known A-ring dienyne with the C,D-ring enol triflates, obtained from the corresponding Grundmann ketones.

Effect of Diamine Bridge on Reactivity of Tetradentate ONNO Nickel(II) Complexes.

Two new square planar ONNO nickel(II) complexes C2_core and C3_core have been synthesized and characterized by single crystal X-ray diffraction, NMR spectroscopy, thermogravimetry, and DFT calculations. The experimental results revealed the effect of the length of diamine bridge in the ligand on the behavior of the studied complexes in the reaction with N-heterocyclic aromatic amines, while DFT calculations provided a basis for the rationalization of this observation. The complex with propylenediamine bridge (C3_core) readily reacts with pyridine and its derivatives to form high-spin (paramagnetic) complexes with octahedral geometry as characterized by X-ray diffraction; electron-donating substituents on the pyridine ring facilitate the coordination of axial ligands.

Design, synthesis and biological evaluation of novel 2-alkylidene 19-norcalcitriol analogs.

Continuing our studies aimed at A-ring modified vitamin D compounds, we designed novel 19-norcalcitriol derivatives bearing at C-2 pegylated chains of different lengths. The terminal fragments of these substituents contain hydroxyls or moieties possessing nitrogen and/or sulfur atoms capable of transition metal ions complexation. Also, two conjugate-type platinum(II) complexes of 19-norcalcitriol were obtained in which l-methionine served as chelating moiety.

Synthesis and Biological Activity of 2,22-Dimethylene Analogues of 19-Norcalcitriol and Related Compounds.

Continuing our search for vitamin D analogues, we explored the modification of the steroidal side chain and inserted a methylene moiety in position C-22 together with either lengthening the side chain or introducing a ring at the terminal end. Our conformational studies confirmed that the presence of a methylene group attached to C-22 restricts the conformational flexibility of the side chain, which can result in changes in biological characteristics of a molecule. All synthesized 1α,25-dihydroxy-2,22-dimethylene-19-norvitamin D analogues proved equal to calcitriol in their ability to bind to the vitamin D receptor, and most of them exert significantly higher differentiation and transcriptional activity than calcitriol.

Synthesis of Gemini analogs of 19-norcalcitriol and their platinum(II) complexes.

Hormonally active vitamin D metabolite, calcitriol, plays an important role in calcium-phosphate homeostasis, immune system actions and cell differentiation. Although anticancer activity of calcitriol is well documented and thousands of its analogs have been synthesized, none has been approved as a potential drug against cancer. Therefore, we attempted to introduce the cytotoxic effect to the calcitriol molecule by its linking to cisplatin.

Synthesis of New Cisplatin Derivatives from Bile Acids.

A series of bile acid derived 1,2- and 1,3-diamines as well as their platinum(II) complexes were designed and synthesized in hope to get a highly cytotoxic compound by the combination of two bioactive moieties. All complexes obtained were subjected to cytotoxicity assays in vitro and some hybrid molecules showed an expected activity.

Structural analysis of 25-hydroxycholesterol stereoisomers differing in configuration in position 17 and 20, by three-dimensional NMR spectra.

The application of 3D NMR experiments and DFT calculations enabled the structure investigation of C-17 epimer of 3-(25-hydroxycholest-5-enyl) acetate is presented. The H-17 and H-20 protons features the same values of H chemical shift, what causes that the structure elucidation require additional resolution enabled by 3D NMR experiments. The NMR experiments and theoretical calculations allowed for: the resonance assignment (3D COSY-HMBC and 3D TOCSY-HSQC techniques), the prediction of spatial structure (3D NOESY-HSQC and 3D ROESY-HSQC experiments), and the precise measurement of heteronuclear coupling constants (3D HSQC-TOCSY spectra with E.

Synthesis of 19-norcalcitriol analogs with pegylated alkylidene chains at C-2.

The results presented in this paper constitute an extension of our synthetic efforts focused on 19-norvitamin D compounds possessing elongated 2-alkylidene substituents. Based on our previous results, molecular modeling studies, and docking experiments, we selected a novel 19-norcalcitriol analog with long chain at C-2 containing several ether moieties and terminated by 2-(pyridin-2'-yl)ethylamino fragment. It was expected that such structural modification might allow binding of transition metal by the ligand, increase solubility of the formed complexes as well as improve their affinity to the VDR.

Seco-B-Ring Steroidal Dienynes with Aromatic D Ring: Design, Synthesis and Biological Evaluation.

Continuing our structure-activity studies on the vitamin D analogs with the altered intercyclic seco-B-ring fragment, we designed compounds possessing dienyne system conjugated with the benzene D ring. Analysis of the literature data and the docking experiments seemed to indicate that the target compounds could mimic the ligands with a good affinity to the vitamin D receptor (VDR). Multi-step synthesis of the C/D-ring building block of the tetralone structure was achieved and its enol triflate was coupled with the known A-ring fragments, possessing conjugated enyne moiety, using Sonogashira protocol.

Synthesis of 19-norcalcitriol analogs with elongated side chain.

Pronounced biological potency of 19-norvitamin D compounds as well as interesting biological action of the vitamin D analogs possessing elongated side chains encouraged us to expand the scope of our structure-activity studies to encompass such modifications of the 1α,25-(OH)D (calcitriol) molecule. The aim of our studies was the synthesis of calcitriol analog, designed on the basis of results of molecular modeling and docking experiments, and characterized by a presence of a long, nitrogen-containing substituent attached to carbon 26, and an exomethylene moiety transferred from C-10 to C-2. The convergent synthesis of such 19-norcalcitriol compound, described in this communication, consisted of the preparation and combining four building blocks.

Synthesis of 19-norcalcitriol analogs with alkylidene moieties at C-2 based on succinic acid and l-methionine.

On the basis of the literature data, our previous research work and docking experiments, we designed novel 19-norvitamin D compounds having elongated 2-alkylidene substituents. These 19-norcalcitriol derivatives have attached 2-(3'-aminopropylidene) substituent in which the nitrogen atom bears acyl residue derived from succinic acid and l-methionine. Both compounds were obtained by the same synthetic strategy involving Julia coupling of the A-ring ketone with the known C/D-ring sulfone.

Design, synthesis and biological properties of seco-d-ring modified 1α,25-dihydroxyvitamin D analogues.

As a continuation of our efforts directed to the structure-activity relationship studies of vitamin D compounds, we present in this paper the synthesis of new analogues of 1α,25-(OH)D characterized by numerous structural modifications, especially a cleaved D ring. Total synthesis of the CD fragment required for the construction of the target vitamins was based on the Stork approach. The structure of the key intermediate - bicyclic hydroxy lactone - was established by crystallographic and electronic circular dichroism (ECD) spectral analysis.

D-seco-Vitamin D analogs having reversed configurations at C-13 and C-14: Synthesis, docking studies and biological evaluation.

Prompted by results of molecular modeling performed on the seco-d-ring-vitamins D, we turned our attention to such analogs, having reversed configurations at C-13 and C-14, as the next goals of our studies on the structure-activity relationship for vitamin D compounds. First, we developed an efficient total synthesis of the "upper" C/seco-d-ring fragment with a 7-carbon side chain. Then, we coupled it with A-ring fragments using Sonogashira or Wittig-Horner protocol, providing the targeted D-seco analogs of 1α,25-dihydroxyvitamin D and 1α,25-dihydroxy-19-norvitamin D possessing a vinyl substituent at C-14 and a double bond between C-17 and C-20.

A new suprasterol by photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3.

The UV-induced photochemical reaction of 1α,25-dihydroxy-9-methylene-19-norvitamin D3 has been investigated. The pentacyclic structure of the isolated product has been unequivocally established by X-ray crystallographic analysis. The possible reaction paths of the examined photochemical transformation are discussed.

Synthesis and Biological Activity of 2-Methylene Analogues of Calcitriol and Related Compounds.

In an attempt to prepare vitamin D analogues that are superagonists, (20R)- and (20S)-isomers of 1α-hydroxy-2-methylenevitamin D3 and 1α,25-dihydroxy-2-methylenevitamin D3 have been synthesized. To prepare the desired A-ring dienyne fragment, two different approaches were used, both starting from the (-)-quinic acid. The obtained derivative was subsequently coupled with the C,D-ring enol triflates derived from the corresponding Grundmann ketones, using the Sonogashira reaction.

Novel 9-Alkyl- and 9-Alkylidene-Substituted 1α,25-Dihydroxyvitamin D3 Analogues: Synthesis and Biological Examinations.

Continuing the structure-activity relationship studies in the vitamin D area, we designed and synthesized novel C-9 substituted calcitriol analogues, possessing different nonpolar groups at this position. 9α-Methyl-1α,25-(OH)2D3, both epimers of 9-methylene-10,19-dihydro-1α,25-(OH)2D3 as well as the parent vitamin with the "reversed" triene system, 9-methylene-19-nor-1α,25-(OH)2D3, were obtained from the previtamin D precursors, constructed by either Suzuki-Miyaura, Sonogashira, or Stille couplings of the corresponding A- and C,D-ring fragments. An alternative synthetic path, leading to the latter vitamin and its homologue with 9-ethylidene group, involved formation of dienynes as precursors of the respective 19-norprevitamin D compounds.

Synthesis and biological activity of two C-7 methyl analogues of vitamin D.

Two novel vitamin D analogues of the hormone 1α,25-(OH)2D3 modified at C-7, namely, 7-methyl-1α,25-(OH)2D3 (12) and 7-methyl-1α,25-(OH)2-19-nor-D3 (26), were synthesized and biologically evaluated to gain further insights into the structure-function relationships of vitamin D. Key steps in the synthesis of 12 include the functionalization at C-7 by an efficient regioselective hydrostannylation of an allene precursor, and the construction of the triene framework by a palladium-catalyzed intramolecular cyclization-Suzuki-Miyaura coupling cascade. Since the calcitriol analogue 12 was prone to conversion into its previtamin D form by thermal equilibration, the corresponding 19-nor-compound 26 was also synthesized.

Synthesis and Biological Activity of 25-Hydroxy-2-methylene-vitamin D3 analogues monohydroxylated in the A-ring.

The 20R- and 20S-isomers of 25-hydroxy-2-methylene-vitamin D3 and 3-desoxy-1α,25-dihydroxy-2-methylene-vitamin D3 have been synthesized. Two alternative synthetic routes were devised for preparation of the required A-ring synthons, starting from the chiral compound derived from the (-)-quinic acid and, alternatively, from the commercially available achiral precursor, monoprotected 1,4-cyclohexanedione. The A-ring dienynes were coupled by the Sonogashira process with the respective C,D-ring fragments, the enol triflates derived from the protected (20R)- or (20S)-25-hydroxy Grundmann ketones.

Synthesis of novel vitamin D3 analog with an additional ring annulated to A and seco-B rings.

A simple method for the synthesis of yet unknown 5E-vitamin D3 analogs with an additional six-membered ring connecting C-6 and C-19 was developed. Ring-closing metathesis (RCM) was used for efficient formation thereof from the corresponding 5E-isomers of 6-alkenyl vitamin D3 compounds which in turn were prepared from the 6-oxo-3,5-cyclovitamin D3. Reinvestigation of the Grignard reactions of this latter compound as well as the following acid-catalyzed cycloreversions showed discrepancies with the literature data describing the course of such processes.

Highly potent 2-methylene analogs of 1α,25-dihydroxyvitamin D3: synthesis and biological evaluation.

As a continuation of our studies on structure-activity relationship of vitamin D compounds we synthesized new calcitriol analogs characterized by the presence of an exomethylene substituent at C-2. The A-ring dienyne synthon was prepared from commercially available quinic acid by two different synthetic routes, and it was then coupled with the triflate enol derived from the corresponding (20R)- and (20S)-Grundmann ketone by palladium catalyzed Sonogashira reaction. The obtained 1α,25-dihydroxy-2-methylene-vitamin D3 analogs, epimeric at C-20, were biologically evaluated by in vitro and in vivo studies.

Synthesis of 9-alkylated calcitriol and two 1α,25-dihydroxy-9-methylene-10,19-dihydrovitamin D3 analogues with a non-natural triene system by thermal sigmatropic rearrangements.

1α,25-(OH)(2)-9α-Methylvitamin D(3) (4), the first known analogue of the natural hormone 1α,25-(OH)(2)D(3) (3) with an alkyl substituent at C-9, and two 1α,25-(OH)(2)-9-methylene-10,19-dihydrovitamin D(3) analogues (7 and 8) with an unprecedented non-natural triene system were synthesized by thermal isomerization of 1α,25-(OH)(2)-9-methylprevitamin D(3) (6). Three alternative approaches (Sonogashira, Stille, or stereoselective dehydration of a tertiary propargyl alcohol) have been successfully used to construct the dienyne precursors of previtamin 6 possessing two methyl groups capable of participating in the [1,7]-sigmatropic hydrogen shift.