Synthesis and Evaluation of Chromogenic and Fluorogenic Analogs of Glycerol for Enzyme Assays

The branched glycerol analogs 1 and 2 were prepared. Mono‐ester derivatives of these triols undergo a chromogenic or fluorogenic reaction in the presence of NaIO₄. In contrast, both the diesters and the triols are themselves not chromogenic or fluorogenic. Diester derivatives of these triols can be used as probes for lipases. The tris‐phosphate derivative of 1 is a fluorogenic substrate for various phosphatases.     

Enzyme activity fingerprinting with substrate cocktails

In the postgenomic era, emphasis is shifting from protein identification to protein functional analysis. Enzyme function can be characterized by measuring activity across series of substrates, which generates an activity profile or fingerprint. Activity fingerprinting is particularly useful to differentiate closely related enzymes. Previously reported fingerprinting methods use series of parallel measurements, which are complex and difficult to reproduce. Here we report a new method for fingerprinting enzyme activities based on using mixtures of substrates, or substrate cocktails, in a single reaction that is then analyzed by HPLC. The fingerprints produced are highly reproducible and allow functional differentiation and classification of closely related enzymes, as demonstrated for a series of lipases and esterases. The method is practical, general, and flexible in terms of reaction conditions and can be adapted to any reaction type.     

Inhibition of mitosis by glycopeptide dendrimer conjugates of colchicine

Glycopeptide dendrimers have been prepared bearing four or eight identical glycoside moieties at their surface (beta-glucose, alpha-galactose, alpha-N-acetyl-galactose, or lactose), natural amino acids within the branches (Ser, Thr, His, Asp, Glu, Leu, Val, Phe), 2,3-diaminopropionic acid as the branching unit, and a cysteine residue at the core. These dendrimers have been used as drug-delivery devices for colchicine. Colchicine was attached to the dendrimers at the cysteine thiol group through a disulfide or thioether linkage. The biological activities of the glycopeptide dendrimer conjugates were evaluated in HeLa tumor cells and non-transformed mouse embryonic fibroblasts (MEFs). The concentrations of glycopeptide dendrimer drug conjugates required to achieve inhibition of cell proliferation by interference with the tubulin system were found to be higher (IC50 > 1 microM) compared to the required colchicine concentration. On the other hand, the glycopeptide dendrimer conjugates inhibited the proliferation of HeLa cells 20-100 times more effectively than the proliferation of MEFs. In comparison, non-glycosylated dendrimers and colchicine itself showed a selectivity of 10-fold or less for HeLa cells.     

Transfer Mechanism of Ionic Drugs: Piroxicam as an agent facilitating proton transfer

Facilitated proton transfer may be of potential significance in pharmacokinetic and pharmacodynamic processes. Here, we show that the NSAID piroxicam and its N-and O-methylated derivatives act as ionophores for proton transfer across the H₂O/1,2-dichloroethane interface. Investigations by cyclic voltammetry showed that the proton transfer occurs by interfacial protonation of the ionophore. The dissociation constants of the three compounds in the organic phase were calculated by Matsuda's theory. With this particular transfer mechanism, the present study exemplifies how electrochemistry at a liquid/liquid interface can be applied to calculate the fundamental thermodynamic parameters related to the pharmacokinetic behavior of ionic drugs.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.     

High stereocontrol in aldol reaction with ketones: enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate aldol reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters.     

Theoretical investigation of the origins of catalysis of a retro-Diels-Alder reaction by antibody 10F11

The antibody 10F11 catalyzes a retro-Diels-Alder reaction that forms HNO. Deductions about the mechanism of catalysis were made by Reymond, Baumann et al. from X-ray crystal structures and from kinetic measurements for mutated antibodies. We report a study of these reactions with quantum mechanical methods and a study of the substrate and transition state binding to the active site of the antibody 10F11 using density functional theory and empirical docking methods. We have quantitated the likely contributions to catalysis of three residues identified as possible causes of catalysis: Trp H104, Phe H101, and Ser H100. Trp H104 can make a significant contribution to catalysis through dispersive interactions (pi-stacking aromatic-aromatic stabilization). On its own, Phe H101 makes only a small contribution to catalysis. When both aromatic residues are present, they act cooperatively and can make greater contributions to catalysis than expected for each residue alone. Ser H100 and the backbone NH of Phe H101 are expected to act through hydrogen bonding to speed up the reaction, but our calculations suggest that they make only a small contribution to catalysis. Reymond's studies suggest that the hydrogen-bonding network may be mediated through a water molecule in the binding site.