Annaliese K. Franz

Organosilicon Molecules with Medicinal Applications

The incorporation of silicon and synthesis of organosilicon small molecules provide unique opportunities for medicinal applications. The biological investigation of organosilicon small molecules is particularly interesting because of differences in their chemical properties that can contribute to enhanced potency and improved pharmacological attributes. Applications such as inhibitor design, imaging, drug release technology, and mapping inhibitor binding are discussed.

An improved high-throughput Nile red fluorescence assay for estimating intracellular lipids in a variety of yeast species

A rapid and inexpensive method for estimating lipid content of yeasts is needed for screening large numbers of yeasts samples. Nile red is a fluorescent lipophilic dye used for detection and quantification of intracellular lipid droplets in various biological system including algae, yeasts and filamentous fungi. However, a published assay for yeast is affected by variable diffusion across the cell membrane, and variation in the time required to reach maximal fluorescence emission. In this study, parameters that may influence the emission were varied to determine optimal assay conditions. An improved assay with a high-throughput capability was developed that includes the addition of dimethyl sulfoxide (DMSO) solvent to improve cell permeability, elimination of the washing step, the reduction of Nile red concentration, kinetic readings rather than single time-point reading, and utilization of a black 96-well microplate. The improved method was validated by comparison to gravimetric determination of lipid content of a broad variety of ascomycete and basidiomycete yeast species.

Cooperative hydrogen-bonding effects in silanediol catalysis.

The importance of cooperative hydrogen-bonding effects and SiOH-acidification is described for silanediol catalysis. NMR binding, X-ray, and computational studies provide support for a unique dimer resulting from silanediol self-recognition. The significance of this cooperative hydrogen-bonding is demonstrated using novel fluorinated silanediol catalysts for the addition of indoles and N,N-dimethyl-m-anisidine to trans-β-nitrostyrene.

Triacylglycerol profiling of marine microalgae by mass spectrometry

We present a method for the determination of triacylglycerol (TAG) profiles of oleaginous saltwater microalgae relevant for the production of biofuels, bioactive lipids, and high-value lipid-based chemical precursors. We describe a technique to remove chlorophyll using quick, simple solid phase extraction (SPE) and directly compare the intact TAG composition of four microalgae species (Phaeodactylum tricornutum, Nannochloropsis salina, Nannochloropsis oculata, and Tetraselmis suecica) using MALDI time-of-flight (TOF) mass spectrometry (MS), ESI linear ion trap-orbitrap (LTQ Orbitrap) MS, and 1H NMR spectroscopy. Direct MS analysis is particularly effective to compare the polyunsaturated fatty acid (PUFA) composition for triacylglycerols because oxidation can often degrade samples upon derivatization. Using these methods, we observed that T. suecica contains significant PUFA levels with respect to other microalgae. This method is applicable for high-throughput MS screening of microalgae TAG profiles and may aid in the commercial development of biofuels.

Silanediol Hydrogen Bonding Activation of Carbonyl Compounds

Silicon is the second most abundant element on the earth s surface, whereby inorganic silanols (SiOH) make up the reactive hydroxyl groups on the surface of minerals, zeolites, and silica gel. The acidic silanol groups are known to be capable of hydrogen bonding to small molecules for heterogeneous catalysis and separation chemistry, but the discrete surface-molecule interactions are not well understood. Silanediols R2Si(OH)2 are of particular interest as they contain a geminal diol bonding motif that is not commonly accessible for carbon analogues, but they represent a synthetic challenge due to their rapid rates of self-condensation. While condensation is advantageous for the synthesis of siloxane polymers, metallosiloxanes, and silesquioxanes, it creates a barrier that may hinder researchers from exploring the properties and applications of discrete silanediols. Recent studies demonstrate that silanols can function as isosteres and transition-state analogues in drug design, in which the enhanced acidity of the silanol can improve binding to a receptor. Small molecules containing silanol and silanediol groups may be useful as models to understand local surface sites and reactivity of silica materials for catalysis, and also to design new homogeneous small-molecule catalysts. We seek to understand the hydrogen bonding patterns and interactions between organic silanediols with carbonyls for applications to catalysis and molecular recognition. Hydrogen bonding interactions play an important role in molecular recognition and metal-free catalysis, and are frequently used in nature for structural organization and enzyme activity. Previous structural studies have demonstrated the hydrogen bonding networks that silanediols can attain through dual donor and acceptor interactions, and also the ability to hydrogen bond with chloride anions for molecular recognition. Studies of silanetriols have shown that amines can complex with and stabilize silanetriols. Here we describe the synthesis and structural studies of organic silanediols for small-molecule hydrogen bonding activation of carbonyl compounds. We are particularly interested in studying bulky silanediols that do not readily undergo condensation reactions. We have performed crystallization and NMR-binding experiments to investigate the hydrogen bonding interactions in both solid-state and solution for molecular recognition and the design of new catalysts. This is the first study of neutral Lewis basic carbonyl compounds with silanediols. We have synthesized a series of bulky silanediols 2–4 that incorporate electron-withdrawing groups to enhance acidity while incorporating steric effects to overcome condensation reactions. Due to the synthetic challenge, the chemical space

Scandium(III)-catalyzed enantioselective allylation of isatins using allylsilanes.

The scandium(III)-catalyzed enantioselective Hosomi-Sakurai allylation of isatins with various substituted allylic silanes is described. A catalyst loading as low as 0.05 mol % is utilized at room temperature to afford the 3-allyl-3-hydroxy-2-oxindoles in excellent yields and enantioselectivity up to 99% ee, including a demonstration of a gram-scale reaction. The effects of additives and varying silyl groups were explored to demonstrate the scope and application.

Phenotypic Screening with Oleaginous Microalgae Reveals Modulators of Lipid Productivity

Here we describe the first phenotypic screening with microalgae to study lipid metabolism and to discover organic small molecules as chemical triggers that increase growth and lipid production. A microplate assay has been developed for analysis of intracellular lipids using Nile Red fluorescence in order to screen a collection of diverse bioactive organic molecules (e.g., kinase inhibitors) with four strains of oleaginous microalgae (Nannochloropsis salina, Nannochloropsis oculata, Nannochloris sp., and Phaeodactylum tricornutum). Several small molecules identified in microplate screening increased lipid productivity >200% without decreasing growth and biomass production. Selected compounds were further investigated in the context of larger batch culture experiments (e.g., 500 mL) and demonstrated to increase lipid levels (up to 84%) while maintaining or increasing the specific growth rate. Bioactive molecules such as forskolin and quinacrine were identified as promising probes of microalgae lipid pathways. We have also determined that common antioxidants such as epigallocatechin gallate and butylated hydroxyanisole (BHA) increase lipid productivity and may represent new probes of oxidative signaling pathways for photooxidative protection.

Catalytic stereoselective synthesis of diverse oxindoles and spirooxindoles from isatins.

A strategy for the efficient two-step synthesis of triazole derivatives of oxindoles and spirooxindoles is presented. Using a common set of N-propargylated isatins, a series of mechanistically distinct stereoselective reactions with different combinations of nucleophiles and catalysts provide access to diverse hydroxy-oxindoles, spiroindolones, and spirocyclic oxazoline structures. The resulting N-propargylated oxindoles are then converted to triazoles using copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. Overall, this strategy affords a 64-member pilot-scale library of diverse oxindoles and spirooxindoles.

Gas-phase acidity studies of dual hydrogen-bonding organic silanols and organocatalysts.

The fundamental properties of a series of organic monosilanols, silanediols, disiloxanediols, and known hydrogen-bonding organocatalysts have been examined in the gas phase using computational and experimental mass spectrometry methods. The organosilicon diol molecules contain dual hydrogen-bonding groups that were designed as potential hosts and hydrogen-bonding catalysts. Newly measured acidities are reported, and implications regarding solvent effects, catalysis, and molecular recognition are discussed.

Enantioselective and Regioselective Indium(III)-Catalyzed Addition of Pyrroles to Isatins

The indium(III)-catalyzed enantioselective and regioselective addition of pyrroles to isatins is described. The effects of metal and solvent on the reactivity and selectivity are compared and discussed, demonstrating that the indium(III)-indapybox complex provides the most effective catalyst. A case of divergent reactivity between pyrroles and indoles is presented.