Vinylogous aldol products from chiral crotylsilanes obtained by enantioselective Rh(II) and Cu(I) carbenoid Si-H insertion.

Enantioenriched homoallylic ethers containing a alpha,beta-unsaturated ester (syn-vinylogous aldol products) were directly accessed by Lewis acid catalyzed crotylation utilizing chiral silane 2. The reagents were prepared by enantioselective Si-H insertion to an alpha-diazovinylacetates using Davies' Rh(2)(DOSP)(4) catalyst or chiral Cu(I) Schiff base complex.

Regioselective intramolecular dipolar cycloaddition of azides and unsymmetrical alkynes.

Enantioenriched allenylsilanes are used in three-component propargylation reactions with aldehydes and silyl ethers to form syn-homopropargylic ethers that contain an imbedded azide. These materials then undergo thermally induced intramolecular 1,3-dipolar cycloaddition reactions, resulting in unique fused ring systems containing 1,2,3-triazoles. The ability to modify all three components of the reaction allows for expedient access to compounds containing significant structural and stereochemical variation.

Synthesis of enantioenriched homopropargylic sulfonamides by a three component reaction of aldehydes, sulfonamides, and chiral allenylsilanes.

Enantioenriched allenylsilanes are used as carbon nucleophiles in three-component reactions with in situ generated N-sulfonylimines to selectively form syn-homopropargylic sulfonamides. The reactions proceed with a variety of aldehyde and sulfonamide reaction partners. These novel reaction products are obtained with useful levels of diastereoselectivity, and the axial chirality of the allenylsilane is fully transferred to point chirality, forming products with >97% ee.

Total synthesis of brevisamide.

A convergent synthesis of brevisamide (1) is described based on the application of the crotyl silane-based [4 + 2]-annulation used for the preparation of the advanced oxygenated tetrahydropyran intermediate 2. The side chain bearing a conjugated (E,E)-diene was efficiently constructed under modified Negishi cross-coupling conditions.

Stereocontrolled synthesis of spirooxindoles through Lewis acid-promoted [5 + 2]-annulation of chiral silyl alcohols.

The enantioselective synthesis of stereochemically and structurally diverse spirocyclic oxindoles by [5 + 2]-annulation of chiral crotylsilanes bearing a primary alcohol is described. The annulation products were further elaborated to polycyclic oxindoles by Pd(0) catalysis.

Annulations of enantioenriched allenylsilanes with in situ generated iminium ions: stereoselective synthesis of diverse heterocycles.

Highly enantioenriched allenylsilanes participate in Lewis acid mediated annulations with in situ generated iminium ions derived from tert-butyl carbamate and methyl carbamate to selectively form functionalized 4,5-dihydropyrroles and 4,5-dihyrooxazines, respectively. The dihydropyrrole products were further elaborated in a stereocontrolled vinylsilane terminated cyclization with in situ generated oxonium ions, resulting in pyranopyrroles.

Anionic amphiphilic dendrimers as antibacterial agents.

An anionic amphiphilic dendrimer is reported that possesses increased cytotoxicological potency against prokaryotic cells compared to eukaryotic cells. The half-maximal effective concentration (EC50) for the dendrimer against Bacillus subtilis, a Gram-positive bacterial strain, was measured to be 4.1 x 10(-5) M, while that against human umbilical vein endothelial cells (HUVEC) was more than 36x greater at a value of 1.

Total synthesis of (-)-kendomycin.

An enantioselective synthesis of (-)-kendomycin is described and is based on the application of the organosilane-based [4 + 2]-annulation strategy for the assembly of the C1a-C10 fragment. An underutilized samarium(II) iodide-assisted cyclization (intramolecular Barbier-type reaction) is employed to afford the protected macrocycle.

Cooperativity and biological complexity.

Cooperative binding effects pervade biology. Only a few basic principles are at play, but in different biological contexts cooperativity appears in distinct guises to achieve different ends. Here I discuss some of the manifestations of cooperativity that are most important in biology and drug discovery as they pertain to systems at different levels of complexity and also highlight aspects of this broadly important phenomenon that remain poorly understood.

New ways to target old receptors.

Numerous important drugs target cytokines and growth factors or their receptors. Our understanding of the molecular mechanisms governing receptor activation and signaling has lagged in key areas, however, limiting drug discovery efforts to relatively few basic strategies. Recently, substantial progress has been made on several aspects of this problem.

Total synthesis of the Hsp90 inhibitor geldanamycin.

An enantioselective synthesis of the Hsp90 inhibitor geldanamycin was achieved in 20 linear steps and 2.0% overall yield from 2-methoxyhydroquinone. The synthesis is highlighted by a regio- and stereoselective hydroboration reaction; a Sc(OTf)(3)/Et(3)SiH-mediated pyran ring-opening reaction; an enantioselective crotylation to simultaneously install the C8-C9 (E) -trisubstituted olefin, the C10 and C11 stereocenters; a chelation-controlled asymmetric metallated acetylide addition; and an intramolecular copper(I)-mediated aryl amidation reaction to close the 19-membered macrolactam.

Designing hydrogel adhesives for corneal wound repair.

Today, corneal wounds are repaired using nylon sutures. Yet there are a number of complications associated with suturing the cornea, and thus there is interest in an adhesive to replace or supplement sutures in the repair of corneal wounds. We are designing and evaluating corneal adhesives prepared from dendrimers--single molecular weight and highly branched polymers.

Kinetic discrimination of sequence-specific DNA-drug binding measured by surface plasmon resonance imaging and comparison to solution-phase measurements.

We demonstrate the use of surface plasmon resonance (SPR) imaging for direct detection of small-molecule binding to surface-bound DNA probes. Using a carefully designed array surface, we quantitatively discriminate between the interactions of a model drug with different immobilized DNA binding sites. Specifically, we measure the association and dissociation intercalation rates of actinomycin-D (ACTD) to and from double-stranded 5'-TGCT-3' and 5'-GGCA-3' binding sites.

Total synthesis of herboxidiene/GEX 1A.

A convergent enantioselective synthesis of herboxidiene/GEX 1A (1) is described that features a double stereodifferentiating crotylation, [4 + 2] annulation, and a silicon-based sp2-sp2 cross-coupling to assemble the conjugated diene.

Preparation and use of enantioenriched allenylsilanes for the stereoselective synthesis of homopropargylic ethers.

A convenient procedure for the synthesis of highly enantioenriched allenylsilanes by Johnson orthoester Claisen rearrangement of 1-silyl propargylic alcohols is described. Allenylsilanes are then used as carbon nucleophiles in three-component, Lewis acid mediated additions to in situ generated oxonium ions, resulting in enantioenriched homopropargylic ethers.

Stereochemical and skeletal diversity employing pipecolate ester scaffolds.

[structure: see text] The stereocontrolled synthesis of pyridooxazinones by Mg(OTf)2-promoted epoxide ring-opening with use of chiral pipecolates as nucleophiles is described. Pyridooxazinone products derived from azido-epoxides can be further rearranged to seven-membered pyridodiazepinones by azide reduction. The sequence of functional group interconversions generates diversity through topological and stereochemical variation.

Immobilized hydrogels for screening of molecular interactions.

Spatially arrayed, high-density microarrays enable the rapid assessment of biological recognition events, and this information is of widespread interest for those working in basic research laboratories as well as in the clinic. Today, one can find DNA, protein, or small molecule arrays. Limitations with these systems include covalent modification of the target complement to the array substrate, array- and target-dependent setup conditions, multiple steps, and loss of hydration at the surface.

Total synthesis of bistramide A.

An asymmetric synthesis of the marine metabolite bistramide A is reported. The synthesis relies on the utility of three different organosilane reagents to construct all principle fragments and 8 of the 11 stereogenic centers of the natural product. [structure: see text].

[4 + 2]-annulations of chiral organosilanes: Application to the total synthesis of leucascandrolide A.

Complete details of an asymmetric synthesis of leucascandrolide A (1) are described. The synthesis highlights the use of two diastereoselective [4 + 2]-annulations for the assembly of the functionalized bispyranyl macrolide 3. An efficient assembly and union of the oxazole-containing side chain 4 with macrolide 3 was carried out using a Mitsunobu reaction.

Secondary structure effects on DNA hybridization kinetics: a solution versus surface comparison.

The hybridization kinetics for a series of designed 25mer probe-target pairs having varying degrees of secondary structure have been measured by UV absorbance and surface plasmon resonance (SPR) spectroscopy in solution and on the surface, respectively. Kinetic rate constants derived from the resultant data decrease with increasing probe and target secondary structure similarly in both solution and surface environments. Specifically, addition of three intramolecular base pairs in the probe and target structure slow hybridization by a factor of two.