Conformationally locked isostere of phosphoSer-cis-Pro inhibits Pin1 23-fold better than phosphoSer-trans-Pro isostere

Stereoisomeric cis and trans substrate analogues for Pin1 were designed and synthesized. The central phosphoSer-Pro core of the Pin1 substrate was replaced by cis and trans amide isosteres in Ac-Phe-Phe-pSer-Psi[(Z and E)CH=C]-Pro-Arg-NH(2), 1 and 2, peptidomimetics. They were synthesized on solid phase in 17% yield for the cis analogue 1, and 16% yield for the trans analogue 2. A second trans amide isostere with a C-terminal N-methylamide 3 was synthesized in 7% yield. The protease-coupled Pin1 assay showed that all three compounds inhibited the Pin1 peptidyl-prolyl isomerase (PPIase) enzymatic activity. The cis isostere 1 was 23 times more potent (K(i) = 1.74 +/- 0.08 muM) than its trans counterpart 2 (K(i) = 40 +/- 2 muM) in competitive inhibition of Pin1. These results suggest that the catalytic site of Pin1 binds cis substrates more tightly in aqueous solution. Antiproliferative activity toward the A2780 human ovarian cancer cell line by the cis and trans analogues correlates with Pin1 inhibition results.     

3‐(Arylhydrazono)pentane‐2, 4‐diones and their Complexes with Copper(II) and Nickel(II) — Synthesis and Crystal Structures

A series of new 3‐(arylhydrazono)pentane‐2, 4‐diones ( 1 ‐ 6 ) synthesized from pentane‐2, 4‐dione and diazonium salts of respective anilines using the procedure of Japp‐Klingemann are described. Complexes with Cu^II and Ni^II salts are prepared ( 7 ‐ 10 , respectively). Spectroscopic properties of these compounds have been studied and X‐ray crystal structures of selected hydrazones ( 3 , 4 , 6 ) and of the hydrazone complexes ( 7 ‐ 10 ) are reported. The structures of the uncomplexed hydrazones feature an intramolecular N‐H···O interaction to yield a six‐membered H‐bond ring reflecting preference of the hydrazone tautomeric structure. All the complexes are mononuclear 2:1 (L:M) structures of six‐membered chelate type involving N₂O₂ binding sites that are quadratic arranged but differ in the entire coordination environment dependent on the metal and the ligand substitution including distorted octahedral and quadratic pyramidal coordination geometries in the Cu^II complexes 7 and 8 or nearly regular square planar coordination geometry in the Ni^II complexes 9 and 10 , respectively. In the crystal packings, strong and weak H‐bond interactions cause supramolecular network structures.     

Crystalline inclusion compounds derived from bulky organosilicon hosts – design, synthesis, structure and stability

New organosilicon compounds 1–3 featuring bulky triphenylsilyl moieties attached to rigid linear or trigonal spacer units have been synthesized and demonstrated to act as clathrate hosts, yielding crystalline inclusion compounds mostly with apolar and aprotic dipolar guest molecules, while the nonbulky dimethylphenylsilyl or trimethylsilyl substituted analogous compounds 4 and 5, which were also synthesized, proved inefficient. X-ray crystal structures of the inclusion compounds 1·DMF (1:1), 1·pyridine (1:1), 2·1,4-dioxane (2:1), 2·pyridine (2:1), 2·p-xylene (2:1), 2·H₂O (2:1) as well as of the unsolvated compounds 2 and 5 are described, and thermal stability studies of selected clathrates are reported.     

Steric course of some cyclopropanation reactions of L-threo-hex-4-enopyranosides

Completely protected 4-deoxy-α-L-threo-hex-4-enopyranosides 1c,d undergo the dichlorocarbene addition affording exclusively diastereomeric adducts 5c,d with the cyclopropane ring anti to the C-3 alkyloxy substituent, while the reaction with 3-unprotected derivatives 1a,b affords a mixture of syn and anti derivatives. Under the Simmons-Smith cyclopropanation adducts 2a-d with a syn stereochemistry are obtained. Starting from 5b, the cyclopropanated sugar 3b is obtained by reduction with LiAlH₄, thus the two diastereomers 2b and 3b can be stereoselectively obtained through the two different pathways. For a useful comparison, 4-deoxy-β-L-threo-hex-4-enopyranoside 1e was also subjected to the above two cyclopropanation methods affording the expected cycloadduct 2e and a diastereomeric mixture of dichlorocycloadducts 4e and 5e (4e/5e=2.8:1).     

Liquid chromatographic determination of S-adenosyl-L-methionine in dietary supplement tablets

A simple and reliable liquid chromatographic method was developed for the determination of S-adenosyl-L-methionine (SAM) in dietary supplement tablets. SAM in products was extracted with a phosphate buffer and separated from the mixture on a reversed-phase C8 column by ion-pair chromatography. A gradient mobile phase containing phosphate buffer, sodium octanesulfonate as the ion-pair reagent, and acetonitrile at a flow rate of 1.2 mL/min was used in the analysis. The UV detection wavelength was set at 257 nm. The calibration curve was linear over a range of 75-375 microg/mL for the SAM active ion with R2 = 0.9999. Replicate tests indicated good reproducibility of the method with a relative standard deviation of 0.9% (n = 8). The multiple extractions and recoveries from fortified products showed the high accuracy of the analysis. The use of the acidic buffer for SAM extraction and elution and the use of a fresh standard for each calibration to counteract the instability of the SAM compound significantly improved the accuracy of the method.     

Supramolecular behaviour of bulky arylboranes in the crystalline state

The aromatic monoboranes 1, 2 and bisboranes 3, 4 of which 4 is a newly synthesised compound have been studied with reference to their supramolecular behaviour in the crystalline state. While the monoboranes crystallise purely, the bisboranes form channel-type solvent inclusions with m-xylene (3a) and nitrobenzene (4a) in the crystals, showing their potential as clathrate hosts in the realm of optically and electronically interesting compounds.     

The Plateau-Douglas problem for nonorientable minimal surfaces

In this paper, the solution of the Plateau-Douglas problem is presented for nonorientable minimal surfaces of higher genus in Riemannian manifolds.     

Experimental and in silico characterization of a biologically active inosose

Inositols have been recently reported to show a biological activity as inhibitors of both glycosidase and amyloid-β protein. After having harvested good crystals suitable for single crystal X-ray diffraction, we performed a comparison with the data inferred by means of a molecular dynamics simulation, based on the use of an appropriate Force Field coupled to the most performing charging scheme. This approach allowed a detailed analysis extended to ultra-fine details, such as atomic displacement parameters. It confirmed the good validity of a robust approach already tested by us in previous studies. A NMR analysis of the molecule in solution was also carried out, to compare the structural findings suggested by the X-ray analysis with the ones in solution and avoid confining them to the solid-state. In this framework, we investigated the above-mentioned inhibiting activity of a class of inososes, by means of a molecular docking investigation, which proved the suggested validity of the studied compound as inhibitor of the α-glucosidase.     

Efficient Differentiation of the Hydroxyl Groups of 3,4-O-Isopropylidene-D-Galactopyranosides by Lipase Catalyzed Esterification and De - Esterification

Abstract

The Pseudomonas sp. (LPS) promoted acyl transfer from vinyl acetate to selected 3,4-O-isopropylidene-D-galactopyranosides takes place in a completely selective manner giving in high yield the corresponding 6-O-acetates. The acetylation rate is strongly dependent on the type and the orientation of the aglycon, varying from a maximum of reactivity for the 1-deoxy derivative, 1,5-anhydro-3,4-O-isopropylidene-D-galactitol (1d), to a minimum for β configurated alkyl glycosides and showing a complete loss of reactivity for 3′,4′:2,3:5,6-tri-O-isopropylidenelactose dimethyl acetal (1e). The latter compound is, however, selectively 6′-O-esterified in good yield by lipase from Candida Antarctica and vinyl acetate. Also the course of the enzymatic hydrolysis of 2,6-di-O-acetyl-3,4-O-isopropylidene-D-galactopyranosides 2 is dependent on the type of the aglycon, both for the reaction rate and the selectivity. The 2-O-acetates 4 are selectively obtained in good yields with porcine pancreatic lipase (PPL) promoted hydrolysis in the case of β and α-methyl, and 1-deoxy derivatives (2a, 2b and 2d), while for β-benzyl (2c) and lactose (2e) analogues satisfactory results are obtained with lipase from Mucor miehei (IM20).

     

Crystal structures of a calix[4]arene controlled by two affixed pyrene units

The synthesis and crystal structures of a calix[4]arene (1) with two affixed pyrene units and its corresponding inclusion compound with chloroform (1a) are reported. In both cases, stacking structures resulting from the influencing control of the pyrene units are observed. The occurrence of infinite or dimeric stack motifs of the pyrene units is dependent on the absence or presence of the included guest solvent.