Tandem Prins/Wagner/Ritter process for the stereoselective synthesis of (3-oxabicyclo[4.2.0]octanyl)amide and (1-(5-aryltetrahydrofuran-3-yl)cyclobutyl)amide derivatives.

Three-component coupling of aldehydes, vinylcyclopropyl carbinols, and nitriles in the presence of 10 mol% TMSOTf at -40 to 0 °C in dichloromethane affords a novel class of (3-oxabicyclo[4.2.0]octanyl)amides in high yields with excellent selectivity, whereas (1-vinylcyclobutyl)methanol provides the corresponding (1-(5-aryltetrahydrofuran-3-yl)cyclobutyl)amides under similar conditions. This is the first report on the synthesis of oxabicycles through a sequential Prins/Wagner/Ritter process.

Tandem Prins/pinacol reaction for the synthesis of oxaspiro[4.5]decan-1-one scaffolds.

A novel Lewis acid catalyzed Prins/pinacol cascade process has been developed for the synthesis of 7-substituted-8-oxaspiro[4.5]decan-1-ones in good yields with excellent selectivity. This is the first example of the synthesis of oxaspirocycles from aldehydes and 1-(4-hydroxybut-1-en-2-yl)cyclobutanol through a cascade of Prins/pinacol rearrangement. This method is applicable to a wide range of aldehydes such as aromatic, aliphatic, heteroaromatic, and α,ß-unsaturated aldehydes.

Synthesis of new cis-fused tetrahydrochromeno[4,3-b]quinolines and their antiproliferative activity studies against MDA-MB-231 and MCF-7 breast cancer cell lines.

New cis-fused tetrahydrochromeno[4,3-b]quinolines have been synthesized by intramolecular [4+2] imino-Diels-Alder reactions of 2-azadienes derived in situ from aromatic amines and 7-O-prenyl derivatives of 8-formyl-2,3-disubstituted chromenones in the presence of 20mol% Yb(OTf)(3) in acetonitrile under reflux conditions in good to excellent yields. The structures were established by spectroscopic data and further confirmed by X-ray diffraction analysis. These compounds were evaluated for their antiproliferative activity against MDA-MB-231 and MCF-7 breast cancer cells. The results showed that compounds 3e, 3f, and 3k exhibit significant antiproliferative activity against MCF-7 breast cancer cells and low inhibitory activity against MDA-MB-231 breast cancer cell lines. Compound 3h displayed activity as comparable to tamoxifen on both the cell lines.

Oleanane-type isomeric triterpenoids from Barringtonia racemosa.

Two new isomeric acylated oleanane-type triterpenoids along with three known compounds were isolated from the MeOH extract of the dried fruits of Barringtonia racemosa. On the basis of spectroscopic methods, with special emphasis on 1D and 2D NMR techniques as well as chemical methods, the structures were characterized as racemosol A (1) [22alpha-acetoxy-3beta,15alpha,16alpha,21beta-tetrahydroxy-28-(2-methylbutyryl)olean-12-ene] and isoracemosol A (2) [21beta-acetoxy-3beta,15alpha,16alpha,28-tetrahydroxy-22alpha-(2-methylbutyryl)olean-12-ene]. The isolated compounds (1-5) were not active against HeLa and P388 D1 carcinoma cell lines.

SUBTLE CONTROL IN SOLUTION AND CRYSTAL STRUCTURES WITH WEAK HYDROGEN BONDS: THE UNUSUAL PROFILE OF DIMETHYL 3, 12-DIOXO-7, 8 DITHIA 4, 11-DIAZABICYCLO[12.2.2]OCTADECA-1(16), 14, 17-TRIENE 5, 10-DICARBOXYLATE (TDA1).

The structural features of the title compound were determined or examined by three diverse procedures: single crystal X-ray diffraction analysis, solution spectroscopic procedures and Quantum mechanical theoretical calculations. The conformational asymmetry of the macrocycle provides the opportunity to form one strong NH···OC intermolecular hydrogen bond, as well as, a number of weak CH···OC bonds. The interior of the macrocycle has short approaches for NH(...)π and NH···S. The many weak hydrogen bonds cooperate to form a very hard, robust crystal. Crystal parameters: C(18)H(22)N(2)O(6)S(2), P2(1)2(1)2(1), a = 5.108(1) Å, b = 18.948(4) Å, c = 21.029(3) Å, α = ß = γ = 90°. Quantum chemical calculations have provided a strong foundation for weak hydrogen bonds. Contrary to popular belief the present work has conclusively proved that the importance of weak hydrogen bonds are perhaps underestimated since calculations show that the energy of duplex are significantly lower then estimated from the identified hydrogen bonding.

Synthesis and biological evaluation of Schizandrin derivatives as potential anti-cancer agents.

A new series of Schizandrin (1) derivatives were synthesized utilizing the C-9 position of the Schizandrin core and evaluated for their cytotoxic activities against HeLa (cervical cancer), A549 (lung cancer), MCF-7 (breast cancer) and DU-145 (prostate cancer) cell lines. Among the synthesized series, 4e, 4f, 4g and 5 showed potent activities against tested cell lines. More significantly, compound 5 exhibited most potent cytotoxic activity against DU-145 with an IC50 value of 1.38 µM which is comparable to the standard agent, doxorubicin. Further, flow cytometry analysis indicated that 5 arrested cells in G2/M phase and consequently leading to apoptosis. Molecular docking analysis showed that 5 occupied the colchicine binding pocket of tubulin. Overall, the present study demonstrates that 5, as a mitotic-agent.

Design, Synthesis, and Characterization of Tyrosinophanes, a Novel Family of Aromatic-Bridged Tyrosine-Based Cyclodepsipeptides.

A simple two-step design strategy has been developed for the synthesis of a large variety of a new class of tyrosine-based aromatic (Ph or Pyr) bridged cyclodepsipeptides (tyrosinophanes). The design is flexible with respect to the size of the ring and the nature of the bridging unit and permits the incorporation of a variety of amino acid residues inside or outside or both inside and outside the ring as illustrated here with the preparation of tyrosine-based macrocycles with aromatic (Ph or Pyr), cage-like alicyclic (adamantane) or simple polymethylene bridging units in ring sizes varying from 26-membered to 78-membered and containing leucine residues as part of the ring or as pendants on the exterior or both inside and outside the macrocyclic ring. (1)H NMR, FT-IR, and CD studies have indicated open-ring structures for these macrocycles. A noteworthy feature of the strategy is the formation of the 1 + 1 + 1 + 1 catenane arising from the interlocking of sebacoyl-bridged tyrosine rings. The potential of tyrosinophanes to serve as simple aromatic hosts in the study of pi-cation type interactions was illustrated with Pyr-bridged macrocycles (6b-8b) using N-methylacridinium hexafluorophosphate as the pyridinium guest. The K(assoc) value with 6b was found to be 8.95 x 10(3) M(-)(1).

NMR study of cyclic peptides with renin inhibitor activity.

Several cyclic analogues of renin inhibitors, based on Glu-D-Phe-Lys motif have been investigated by NMR spectroscopy and molecular dynamics calculations (MD). The 15 membered macrocycle, resulting from Glu and Lys side-chain cyclization, exhibits conformational preference. The structural evidence from NMR shows the presence of hydrogen bond between Lys NH and Glu side-chain carbonyl, resulting in a 10 membered pseudo beta-turn-like structure. The structure of the cyclic moiety is similar in all the peptides, which takes at least two conformations around Calpha-Cbeta in Glu side chain. The restrained MD calculations further support such observations and show that the macrocycle is fairly rigid, with two conformations about the Glu Calpha-Cbeta bond. The linear peptide appendages, which are essential for activity in cyclic peptides, show an extended structure in the beta-region of Ramchandran plot. These calculations also demonstrate that for the most active peptide, two major conformers each exist about the Calpha-CO bond of the Lys, D-Trp and Leu residues. In this peptide, the cyclic moiety presents a negatively charged surface formed due to the carbonyl oxygens, which are thus available to form hydrogen bonds with the receptor. The linear fragment presents further binding sites with a surface which has the hydrophobic side chains of D-Trp, Leu and D-Met on one side and carbonyls on the other side.

An unusual novel anti-oxidant dibenzoyl glycoside from Salvinia natans.

An unusual novel and significant anti-oxidant 1,2-dibenzoyl glycoside, natansnin (1), has been isolated from Salvinia natans. The structure of 1 was established by the study of NMR and CD spectral data.