A Short Route to the Synthesis of Digoxose Trisaccharide Glycal Donor via Mislow-Evans Rearrangement.

The Mislow-Evans rearrangement was used as a key reaction to construct digitoxose-derived glycals. The same rearrangement was iteratively performed on di- and trisaccharides to form the digoxose glycal donor component present in the cardenolides digitoxin, digoxin, and gitoxin. The scalability of the trisaccharide synthesis was shown by performing the reactions on a multigram scale. Glycosylation reactions were also performed between the synthesized digoxin glycal donor and aglycons digoxigenin and gitoxigenin to synthesize novel cardenolide derivatives.

A simple and efficient pathway for the total synthesis of marine natural products: bengamide E and 5-epi-bengamide E.

Total synthesis of the marine natural product bengamide E and 5-epi-bengamide E has been accomplished using two routes: (i) via a polyhydroxy acid precursor involving a total of 16 steps with an overall yield of 17.0% and (ii) via a cyclic lactone precursor with a total of 12 steps and overall 23.0% yield. The key steps involve (1) regioselective p-methoxybenzylidine ring opening, (2) a stereoselective Grignard reaction and (3) olefin cross-metathesis. The total synthesis could provide significant quantities of bengamide E and 5-epi-bengamide E as all the reaction processes were very efficient and the raw materials were inexpensive and highly abundant. The protocol has an advantage over previously reported methods as it provides ready access to the C-5 hydroxy group for further modification and its future structure-activity relationship studies for anti-tumor activity.

A Ring Expansion─Stereoselective Cycloaddition of Carbohydrate-Derived Donor-Acceptor Cyclopropanes: Synthesis of Bridged Oxepanone-Indole Hybrids.

An efficient method for the construction of sugar-derived chiral oxepanone-indole molecular hybrids is investigated. The reaction condition is optimized by monitoring the progress at various temperatures, with various solvents, and with different Lewis acid catalysts. Under optimized conditions, high stereoselectivity and efficiency are achieved in most of the formed cycloadducts. The accessibility of the strategy is evaluated by utilizing an array of carbohydrate-derived donor-acceptor cyclopropanes and variably substituted indole substrates. Additionally, quick access to the bridged indole-oxepanone framework is described by utilizing a diastereoselective (3+2) cycloaddition of aryl-substituted donor-acceptor cyclopropanes incorporated in a pyran ring.

[1,2]- vs [2,3]-Wittig Rearrangement in Carbohydrate Derived Alkenyl Systems.

A simple and efficient strategy for the regio- and stereoselective synthesis of carbon-branched sugar derivatives is described. The successful implementation of Wittig rearrangement on substrates derived by Ferrier rearrangement of various glycals and 3-O-alkenyl glycals is studied extensively. A highly selective [1,2]- or [2,3]-Wittig rearrangement is revealed that provides a novel class of stereodefined 3-C-branched glycals and C-glycosides, which are otherwise difficult to obtain.

The Effect of Capsaicin Derivatives on Tight-Junction Integrity and Permeability of Madin-Darby Canine Kidney Cells.

Capsaicin is known to interfere with tight junctions (TJs) of epithelial cells and therefore to enhance paracellular permeability of poorly absorbable drugs. However, due to its low water solubility, pungency, and cytotoxicity, its pharmacologic use is limited. In this study, we investigated the effect of capsaicin derivatives of synthetic (e.g., 10-hydroxy-N-(4-hydroxy-3-methoxybenzyl)decanamide, etc.) and natural (olvanil and dihydrocapsaicin) origin on Madin-Darby Canine Kidney-C7 cells. Impedance spectroscopy was used to determine the transepithelial electrical resistance and the capacitance. Permeability assays with fluorescein isothiocyanate-dextran were carried out to evaluate the impact on cell permeability. The results show that lipophilicity could play an important role for the interference with TJ and that the mechanism is independent from the ion channel TRPV-1 and hence on the flux of calcium into the cells. In summary, we synthesized 4 derivatives of capsaicin of lower lipophilicity and compared their properties with other well-known vanilloids. We show that these compounds are able to enhance the permeability of a hydrophilic macromolecule, by opening the TJ for a shorter time than capsaicin. This behavior is dependent on the lipophilicity of the molecule. Understanding of these phenomena may lead to better control of administration of therapeutic molecules.

Synthesis and in vitro anticancer and antitubercular activity of diarylpyrazole ligated dihydropyrimidines possessing lipophilic carbamoyl group.

A series of dihydropyrimidine derivatives were synthesized by utilizing Biginelli reaction and evaluated for their in vitro anticancer activity against MCF-7 human breast cancer (HBC) cell line using sulforhodamine B (SRB) assay and antitubercular activity against Mycobacterium tuberculosis (MTB) H(37)Rv using Microplate Alamar Blue Assay (MABA). Compounds 13p, 13t were exhibited 70.6% and 63.7% of HBC cell growth inhibition at 10 µM concentration. Interestingly compound 13p was also found to be the most potent in the series against MTB H(37)Rv with MIC value of 0.125 µg/mL.

Alpha-lactosylceramide as a novel "sugar-capped" CD1d ligand for natural killer T cells: biased cytokine profile and therapeutic activities.

The invariant natural killer T cells (iNKT) cells have emerged as an important regulator of immunity to infection, cancer, and autoimmune diseases. They can be activated by glycolipids that bind to CD1d. The most effective iNKT ligand reported to date is alpha-galactosylceramide (alpha-GalCer), which stimulates iNKT cells to secrete both Th-1 and Th-2 cytokines. Indiscriminate induction of both types of cytokines could limit the therapeutic potential of iNKT ligands, as Th-1 and Th-2 cytokines play different roles under physiological and pathological conditions. Therefore, a ligand with a biased cytokine-release profile would be highly desirable. Here, we report the synthesis and biological activity of alpha-lactosylceramide (alpha-LacCer). Our data demonstrate that alpha-LacCer can stimulate iNKT cells to proliferate and release cytokines, both in vitro and in vivo. Interestingly, while alpha-LacCer is approximately 1000-times less efficient than alpha-GalCer in inducing Th-1 cytokines, it is as potent as alpha-GalCer in the induction of Th-2 cytokines; therefore, alpha-LacCer is a novel compound that induces a biased cytokine release. Processing by beta-glycosidase was critical for alpha-LacCer activity. Moreover, in vivo experiments suggest that alpha-LacCer is at least as potent as alpha-GalCer in the treatment of tumors and experimental autoimmune encephalomyelitis.

Characterization of a bacterial beta-1,3-galactosyltransferase with application in the synthesis of tumor-associated T-antigen mimics.

T-Antigen (Gal-beta1,3-GalNAc-alpha-O-Ser/Thr) is an important precursor of mucin-type O-glycans. T-Antigen is found to be closely associated with cancer progression and metastasis and has been used to develop carbohydrate-based anticancer vaccines. Enzymatic synthesis of T-antigen disaccharides have relied on the use of beta-1,3-galactosyltransferases recently cloned and characterized from several eukaryotic organisms. However, its application is limited by the difficulty of obtaining homogeneous enzymes and the strict substrate specificity of enzymes. Recently, a number of bacteria have been found to express carbohydrate structures that mimic host glycans. The corresponding glycosyltransferases have been exploited in the facile synthesis of a number of clinically important glycoconjugate mimics. In this study, we biochemically characterized a bacterial beta-1,3-galactosyltransferase (WbiP) from Escherichia coli O127, which expresses a T-antigen mimic in the lipopolysaccharide (LPS) structure. Substrate study showed that WbiP could readily glycosylate a series of N-acetylgalactosamine (GalNAc) analogues with alpha-substitutions at the reducing end, including glycosylated Ser and Thr (GalNAc-alpha-O-Ser/Thr), which illustrates the use of WbiP for the facile synthesis of T-antigens. Alignment of a group of putative bacterial beta-1,3-galactosyltransferases revealed the presence of two conserved DXD motifs, possibly suggesting a different functional role of each motif. Site-directed mutagenesis, enzyme kinetics as well as UDP-bead binding assays were carried out to investigate the role of each DXD motif in WbiP. The results suggest that 88DSD90 is critical in the binding of sugar donor UDP-Gal, whereas 174DYD176 may participate in the binding of the sugar acceptor. This study expands the scope of using bacterial glycosyltransferases as tools for in vitro synthesis of glycoconjugate mimics with clinical significance.

Design and synthesis of novel HIV-1 protease inhibitors incorporating oxyindoles as the P2'-ligands.

A series of novel oxyindole-derived HIV-1 protease inhibitors were designed and synthesized based upon our X-ray crystal structure of inhibitor 2 (TMC-114) bound to HIV-1 protease. The effects of substituents, spirocyclic rings, and ring sizes have been investigated. A number of inhibitors exhibited low nanomolar inhibitory potencies against HIV protease.

A Stereoselective Anti-Aldol Route to (3R,3aS,6aR)-Hexahydrofuro[2,3-b] furan-3-ol: A Key Ligand for a New Generation of HIV Protease Inhibitors.

A stereoselective synthesis of (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-ol, an important high affinity P2-ligand, in high enantiomeric excess (>99%) is reported. The synthesis features an ester-derived titanium enolate based highly stereoselective anti-aldol reaction as the key step.