Dihydroxyacetone variants in the organocatalytic construction of carbohydrates: mimicking tagatose and fuculose aldolases

Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase.

Continuous glucose detection using boronic acid-substituted viologens in fluorescent hydrogels: linker effects and extension to fiber optics

A fluorescent anionic dye and a viologen appended with boronic acids, which serve as glucose receptors, have been synthesized and immobilized into a poly(2-hydroxyethyl methacrylate) hydrogel for use as a continuous glucose monitor. The fluorescence of the dye is modulated by the quenching efficiency of the viologen-based receptor, which in turn is dependent on the glucose concentration. Two monomeric versions of the quencher/receptor unit were prepared and their performance within the hydrogel evaluated. By tethering the quencher/receptor to the hydrogel matrix using a single-point attachment, slightly improved glucose sensing was observed. The hydrogels were tested for their ability to continuously and reversibly detect glucose over the course of several hours. The tests were carried out using a cuvette-based system, as well as a fiber-optic-based configuration. Under physiological conditions (0.1 M phosphate buffer, pH 7.4, 37 degrees C), the fluorescent hydrogels display an excellent dynamic response to glucose concentrations within the biologically significant range (2.5-20 mM).

Organocatalytic Enantioselective Synthesis of Metabotropic Glutamate Receptor Ligands

(R)-Proline catalyzes the amination reaction of functionalized indane carboxaldehydes and allows for the efficient enantioselective synthesis (>99% ee) of the metabotropic glutamate receptor ligands (S)-AIDA and (S)-APICA. [reaction: see text]

Evaluation of pyranine derivatives in boronic acid based saccharide sensing: significance of charge interaction between dye and quencher in solution and hydrogel

In an ongoing program to synthesize a glucose sensing polymer that could be used for real time glucose monitoring in vivo, we have been exploring the use of boronic acid functional viologens as glucose responsive quenchers for fluorescent dyes. The present study focuses on the effect of ionic interactions between pyranine or its various sulfonamide derivatives and the viologen quenchers. Dyes bearing anionic groups were quenched more efficiently when compared to dyes with nonionic substituents. The anionic dyes in conjunction with the cationic quenchers exhibited a broader range of glucose response both in solution and when immobilized in a hydrogel. The interaction of glucose with the sensing components was similar whether they are soluble or immobilized.

Mimicking Dihydroxy Acetone Phosphate-Utilizing Aldolases through Organocatalysis: A Facile Route to Carbohydrates and Aminosugars

[reaction: see text] A practical and environmentally friendly organocatalytic strategy designed to mimic the DHAP aldolases has been developed and shown to be effective in the preparation of carbohydrates and aminosugars. (S)-Proline and (S)-2-pyrrolidine-tetrazole catalyzed the aldol reaction between dihydroxy acetone variants such as 1,3-dioxan-5-one and 2,2-dimethyl-1,3-dioxan-5-one with aldehydes to give the corresponding polyols in good yields with very high ees.

Asymmetric Synthesis of Quaternary α- and β-Amino Acids and β-Lactams via Proline-Catalyzed Mannich Reactions with Branched Aldehyde Donors

[reaction: see text] L-Proline-catalyzed direct asymmetric Mannich reactions of N-PMP protected alpha-imino ethyl glyoxylate with various alpha,alpha-disubstituted aldehydes affords quaternary beta-formyl alpha-amino acid derivatives with excellent yields and enantioselectivities. The Mannich products are further converted to the corresponding quaternary alpha- and beta-amino acids and beta-lactams.