Scott E. Schaus

Chemogenomic profiling on a genome-wide scale using reverse-engineered gene networks

A major challenge in drug discovery is to distinguish the molecular targets of a bioactive compound from the hundreds to thousands of additional gene products that respond indirectly to changes in the activity of the targets. Here, we present an integrated computational-experimental approach for computing the likelihood that gene products and associated pathways are targets of a compound. This is achieved by filtering the mRNA expression profile of compound-exposed cells using a reverse-engineered model of the cells gene regulatory network. We apply the method to a set of 515 whole-genome yeast expression profiles resulting from a variety of treatments (compounds, knockouts and induced expression), and correctly enrich for the known targets and associated pathways in the majority of compounds examined. We demonstrate our approach with PTSB, a growth inhibitory compound with a previously unknown mode of action, by predicting and validating thioredoxin and thioredoxin reductase as its target.

Asymmetric Petasis Reactions Catalyzed by Chiral Biphenols

Chiral biphenols catalyze the enantioselective Petasis reaction of alkenyl boronates, secondary amines, and ethyl glyoxylate. The reaction requires the use of 15 mol % of (S)-VAPOL as the catalyst, alkenyl boronates as nucleophiles, ethyl glyoxylate as the aldehyde component, and 3 A molecular sieves as an additive. The chiral alpha-amino ester products are obtained in good yields (71-92%) and high enantiomeric ratios (89:11-98:2). Mechanistic investigations indicate single ligand exchange of acyclic boronate with VAPOL and tetracoordinate boronate intermediates.

Enantioselective Addition of Boronates to Chromene Acetals Catalyzed by a Chiral Brønsted Acid/Lewis Acid System

Chiral α,β-dihydroxy carboxylic acids catalyze the enantioselective addition of alkenyl- and aryl boronates to chromene acetals. The optimal carboxylic acid is a tartaric acid amide, easily synthesized via a 3-step procedure. The reaction is enhanced by the addition of Lanthanide triflate salts such as cerium(IV)-and ytterbium(III) triflate. The chiral Bronsted acid and metal Lewis acid may be used in as low as 5 mol % relative to acetal substrate. Optimization of the reaction conditions can lead to yields >70% and enantiomeric ratios as high as 99:1. Spectroscopic and kinetic mechanistic studies demonstrate an exchange process leading to a reactive dioxoborolane intermediate leading to enantioselective addition to the pyrylium generated from the chromene acetal.

The Mechanism and an Improved Asymmetric Allylboration of Ketones Catalyzed by Chiral Biphenols

A mechanistic study of the enantioselective asymmetric allylboration of ketones with allyldiisopropoxyborane catalyzed by chiral biphenols resulted in the development of improved reaction process. In a ligand exchange process involving the chiral biphenol and the boronate to liberate isopropanol as the key step, addition of isopropanol to the reaction was found to increase the overall rate and enantioselectivity. In the design of an improved reaction, a boronate possessing a tethered alcohol would more readily liberate catalyst at the end of a reaction. The use of allyldioxaborinane with 2 mol% (S)-3,3′-Br2-BINOL and 2 equivalents t-BuOH relative to ketone at room temperature results in high yields and enantioselectivities. Insight gathered from the mechanistic investigation resulted in the development of a reaction process that uses less catalyst (from 15 mol% to 2 mol%) at warmer temperatures (from -35 °C to room temperature).

Enantioselective synthesis of SNAP-7941: chiral dihydropyrimidone inhibitor of MCH1-R.

An enantioselective synthesis of SNAP-7941, a potent melanin concentrating hormone receptor antagonist, was achieved by using two organocatalytic methods. The first method utilized to synthesize the enantioenriched dihydropyrimidone core was the Cinchona alkaloid-catalyzed Mannich reaction of beta-keto esters to acylimines and the second was the chiral phosphoric acid-catalyzed Biginelli reaction. Completion of the synthesis was accomplished via selective urea formation at the N3 position of the dihydropyrimidone with the 3-(4-phenylpiperidin-1-yl)propylamine side chain fragment. The synthesis of SNAP-7921 highlights the utility of asymmetric organocatalytic methods in the construction of an important class of chiral heterocycles.

Dynamic kinetic resolution of epichlorohydrin via enantioselective catalytic ring opening with TMSN3. Practical synthesis of aryl oxazolidinone antibacterial agents

Abstract The dynamic kinetic resolution of racemic epichlorohydrin has been achieved via enantioselective asymmetric ring opening with TMSN3 catalyzed by the (salen)Cr(III)N3 complex 1. The resulting 3-azido-1-chloro-2-trimethylsiloxypropane product was obtained in high enantiomeric purity and incorporated into the synthesis of U-100592, a representative from a class of highly-promising aryl oxazolidinone antibacterial agents.

Enantioselective Addition of Boronates to Acyl Imines Catalyzed by Chiral Biphenols

On the big screen: A chiral biphenol catalyst screening protocol was developed for the rapid identification of enantioselective nucleophilic boronate reactions with acyl imines (see scheme). The approach successfully identified a unique catalyst for the reaction of aryl, vinyl, and alkynyl boronates. Mechanistic studies demonstrate boronate ligand exchange with the catalyst is necessary for activation towards nucleophilic addition.

Catalytic Diastereoselective Petasis Reactions

Multicomponent Petasis reactions: the first diastereoselective Petasis reaction catalyzed by chiral biphenols that enables the synthesis of syn and anti β-amino alcohols in pure form has been developed. The reaction exploits a multicomponent approach that involves boronates, α-hydroxy aldehydes, and amines.

Carbenoid insertions into the siliconhydrogen bond catalyzed by chiral copper (I) schiff base complexes

Abstract An asymmetric insertion reaction of α-diazoesters derived from methyl arylacetates into the silicon-hydrogen bond of silanes was achieved using a copper (I) catalyst associated with a chiral, C 2 symmetric Schiff base. Addition of the diazoesters 1 (1 equiv) to the Cu·Lig complex (R,R) - 3 (0.1 equiv) in the presence of the silane reagent (1.5 equiv) at −40° C yielded the corresponding insertion products 2 or 4 in good yields with varying levels of selectivity (up to 84% ee).

Enantioselective boronate additions to N-acyl quinoliniums catalyzed by tartaric acid.

Tartaric acid catalyzes the asymmetric addition of vinylboronates to N-acyl quinoliniums, affording highly enantioenriched dihydroquinolines. The catalyst serves to activate the boronate through a ligand-exchange reaction and generates the N-acyl quinolinium in situ from the stable quinoline-derived N,O-acetal.