Synthesis of 25-Hydroxy-provitamin D3 by Direct Hydroxylation of Protected 7-Dehydrocholesterol.

A new synthetic route to 25-hydroxy-provitamin D3 was elaborated. The synthesis consists of direct hydroxylation at C-25 of 7-dehydrocholesterol hetero Diels-Alder adducts. The adducts were prepared by [4 + 2] cycloaddition of azadienophiles to the steroidal diene. The hydroxylation reactions of adducts were carried out with different dioxiranes or with chromyl trifluoroacetate. The byproducts of these reactions were isolated and identified. The strengths and weaknesses of hydroxylation methods with different oxidizing agents were discussed.

A Simple Four-Step Synthesis of the Potato Alkaloid Demissidine from the Common Sapogenin Tigogenin.

A simple synthesis method of solanidane alkaloids from common steroidal sapogenins was developed. Previously described multi-step transformations of tigogenin to demissidine (8-12 steps) were shortened to four steps only. The key-step of the present synthesis was the epimerization at C25 of the lactam intermediate. Different approaches to this reaction, i. e., a classical one via enolate, and a chemoselective umpolung transformation, were thoroughly investigated. The epimerization step is unnecessary if the starting sapogenin has the same configuration at C25 as the target alkaloid because the configuration at C25 (either R or S) remains intact throughout the synthesis. Thus, the related solanidane alkaloids, 12ß-hydroxy-25-epi-demissidine and 5-epi-demissidine, were synthesized in the three-step procedure with retention of configuration at this stereogenic center from rockogenin (25R-5α-sapogenin) or sarsasapogenin (25S-5ß-sapogenin), respectively.

Synthesis of Demissidine Analogues from Tigogenin via Imine Intermediates.

A five-step transformation of a spiroketal side chain of tigogenin into an indolizidine system present in solanidane alkaloids such as demissidine and solanidine was elaborated. The key intermediate in the synthesis was spiroimine 3 readily obtained from tigogenin by its RuO4 oxidation to 5,6-dihydrokryptogenin followed by amination with aluminum amide generated in situ from DIBAlH and ammonium chloride. The mild reduction of spiroimine to a 26-hydroxy-dihydropyrrole derivative and subsequent mesylation resulted in the formation of 25-epidemissidinium salt or 23-sulfone depending on reaction conditions.

Phase Transitions and Structural Changes in DPPC Liposomes Induced by a 1-Carba-Alpha-Tocopherol Analogue.

Steady-state emission spectroscopy of 1-anilino-8- naphthalene sulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescence anisotropy, and DSC methods were used to characterize the interactions of the newly synthesized 1-carba-alpha-tocopherol (CT) with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane. The DSC results showed significant perturbations in the DPPC structure for CT concentrations as low as 2 mol%. The main phase transition peak was broadened and shifted to lower temperatures in a concentration-dependent manner, and pretransition was abolished. Increasing CT concentrations induced the formation of new phases in the DPPC structure, leading to melting at lower temperatures and, finally, disruption of the ordered DPPC structure. Hydration and structural changes of the DPPC liposomes using ANS and DPH fluorescent probes, which are selectively located at different places in the bilayer, were studied. With the increased concentration of CT molecules in the DPPC liposomes, structural changes with the simultaneous formation of different phases of such mixture were observed. Temperature studies of such mixtures revealed a decrease in the temperature of the main phase transition and fluidization at decreasing temperatures related to increasing hydration in the bilayer. Contour plots obtained from concentration-temperature data with fluorescent probes allowed for identification of different phases, such as gel, ordered liquid, disordered liquid, and liquid crystalline phases. The CT molecule with a modified chromanol ring embedded in the bilayer led to H-bonding interactions, expelling water molecules from the interphase, thus introducing disorder and structural changes to the highly ordered gel phase.

Synthesis of Solanum Alkaloid Demissidine Stereoisomers and Analogues.

Demissidine is an indolizidine alkaloid isolated from several potato species. A simple synthesis of demissidine stereoisomers and analogues from a common steroidal sapogenin tigogenin is presented in the paper. The key intermediate in the synthesis of these compounds is readily available tigogenoic acid. Its step-by-step transformation to indolizidine yielded 20R,25R or 20R,25S products while the direct reductive amination produced the 20S,25R compound (25-epi-demissidine).

A Convenient Synthesis of (16S,20S)-3ß-hydroxy-5α-pregnane-20,16-carbolactam and its N-alkyl Derivatives.

A concise synthesis of (16S,20S)-3ß-hydroxy-5α-pregnane-20,16-carbolactam from tigogenin via the corresponding lactone is described. The most efficient synthetic route consisted of the lactone ring-opening with aminoalane reagent followed by PDC or Dess-Martin oxidation. The oxo-amide obtained was subjected to cyclization with Et3SiH/TFA or Et3SiH/Bi(TfO)3. Alternately, the lactone was converted first to the oxo-acid, which was then subjected to the microwave-assisted reductive amination. N-Alkyl derivatives were also obtained in a similar way.

Synthesis, DFT Calculations, and In Vitro Antioxidant Study on Novel Carba-Analogs of Vitamin E.

Vitamin E is the most active natural lipophilic antioxidant with a broad spectrum of biological activity. α-Tocopherol (α-T), the main representative of the vitamin E family, is a strong inhibitor of lipid peroxidation as a chain-breaking antioxidant. Antioxidant and antiradical properties of vitamin E result from the presence of a phenolic hydroxyl group at the C-6 position. Due to stereoelectronic effects in the dihydropyranyl ring, the dissociation enthalpy for phenolic O-H bond (BDEOH) is reduced. The high chain-breaking reactivity of α-T is mainly attributed to orbital overlapping of the 2p-type lone pair on the oxygen atom (O1) in para position to the phenolic group, and the aromatic π-electron system. The influence of the O1 atom on the antioxidant activity of vitamin E was estimated quantitatively. The all-rac-1-carba-α-tocopherol was synthesized for the first time. Along with model compounds, 1-carba-analog of Trolox and its methyl ester were screened for their in vitro antioxidant activity by inhibition of styrene oxidation, and for the radical-reducing properties by means of 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH) scavenging assay. To study the antioxidant activity, density functional theory (DFT) was also applied. Reaction enthalpies related to HAT (hydrogen atom transfer), SET-PT (sequential electron transfer-proton transfer), and SPLET (sequential proton loss-electron transfer) mechanisms were calculated.

Chromane helicity rule--scope and challenges based on an ECD study of various trolox derivatives.

The validity of the chromane helicity rule correlating the sense of twist within the dihydropyran ring with the CD sign of the (1)Lb band observed at ca. 290 nm in their electronic circular dichroism (ECD) spectra is examined using a set of natural (S)-trolox derivatives. To investigate both the scope and the limitations of the rule a combination of ECD spectroscopy, especially the temperature dependence of the ECD spectra, single crystal X-ray diffraction analyses, and density functional theory (DFT) calculations was used. A thorough conformational analysis supported by the X-ray data led to the identification of predominant conformers. Then, a comparison of the experimental ECD spectra with the spectra simulated by TDDFT calculations allowed for a reasonable interpretation of the accumulated data. The results clearly indicated that to avoid the possibility of erroneous conclusions the chromane helicity rule should be used with great caution. This is likely related to the conformational flexibility of tested compounds by which conformers of different helicities can be produced. Therefore, based on the results presented here, it is strongly recommended that the conclusions derived from analysis of experimental data are supported with the appropriate theoretical computations.

6-Hy-droxy-2,5,7,8-tetra-methyl-3,4-dihydro-2H-1-benzopyran-2-carbonitrile, from synchrotron data.

The crystal structure of the title compound, C(14)H(17)NO(2), solved and refined against synchrotron diffraction data, contains one formula unit in an asymmetric unit. In the crystal, mol-ecules form right-handed helices located at the 2(1) screw axis parallel to the a-axis direction, generated by O-H⋯N hydrogen bonding between the hy-droxy group and carbonitrile group of an adjacent mol-ecule.

2,2,5,7,8-Penta-methyl-chroman-6-yl 2,3,4,6-tetra-O-acetyl-α-d-glucopyran-oside from synchrotron data.

The crystal structure of the title compound, C(28)H(38)O(11), solved and refined against synchrotron diffraction data, contains two formula units in the asymmetric unit. In both mol-ecules, the dihydro-pyran ring along with its methyl substituents is disordered and adopts two alternative half-chair conformations. The occupancy of the major conformers of the two mol-ecules refined to 0.858 (5) and 0.523 (5).

rac-6-Hy-droxy-2,5,7,8-tetra-methyl-chroman-2-carboxamide from synchrotron data.

The crystal structure of the title water-soluble analogue of vitamin E, trolox amide, C(14)H(19)NO(3), solved and refined against synchrotron diffraction data, contains two mol-ecules in the asymmetric unit. In both molecules, the heterocyclic ring is in a half-chair conformation. The crystal packing features a herring-bone pattern generated by N-H⋯O hydrogen bonds between the hy-droxy and amide groups. O-H⋯O hydrogen bonds also occur.