Andrew Hempel

Participation of Acetylpseudouridine in the Synthesis of a Peptide Bond in Vitro

Uracil, uridine, and pseudouridine were acetylated by refluxing in acetic anhydride, and the products of acetylation were incubated with a synthetic peptide(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21) that corresponds to the N-terminal 21 amino acid residues of human myelin basic protein. Peptide bond formation, at the N terminus in peptide 1-21, was obtained with acetyluracil and acetylpseudouridine, but not with acetyluridine. Transfer of an acetyl group from acetyluracil and acetylpseudouridine depended on acetylation in the N-heterocycle. X-ray crystallographic analysis definitively established N-1 as the site of acetylation in acetyluracil. Mass spectrometry of the acetylation products showed that one acetyl group was transferred to peptide 1-21, in water, by either acetyluracil or acetylpseudouridine at pH 6. Release of the acetyl group by acylaminopeptidase regenerated peptide 1-21 (mass spectrometry) and automated sequencing (for five cycles) of the regenerated (deacetylated) peptide demonstrated that the N terminus was intact. The findings are discussed in the context of a possible role for pseudouridine in ribosome-catalyzed peptidyltransfer, with particular reference being made to similarities between the possible mechanism of acyl transfer by acetyluracil/pseudouridine and the mechanism of carboxyl transfer by carboxylbiotin in acetyl CoA carboxylase. The possibility that idiosyncratic appearance of a wide range of acyl substituents in myelin basic protein could be related to a peculiar involvement of ribosomal pseudouridine is mentioned.

Molecular properties and myocardial salvage effects of morin hydrate

Morin hydrate is a bioactive pigment found in yellow Brazil wood. Recently, we reported that morin hydrate prolongs the survival of three types of cells from the human circulatory system against oxyradicals generated in vitro. The protection excels that given by equimolar concentrations of ascorbate, mannitol, and Trolox. Here, we demonstrate that, in vivo, morin hydrate at 5 mumol/kg actually reduced by > 50% the tissue necrosis in post-ischemic and reperfused rabbit hearts. Mechanistically, morin hydrate not only scavenges oxyradicals, but also moderately inhibits xanthine oxidase, a free-radical generating enzyme from the ischemic endothelium. Among other possibilities, morin hydrate appears to chelate some metal ions (e.g. Fe2+) in oxyradical formation, although this needs to be examined further. Nuclear magnetic resonance (at 500 mHz) and electron-impact mass spectrometry also supported a molecular formula of C15H10O7 for morin hydrate. Only by X-ray crystallography was it clearly revealed that there are two water molecules attached by intermolecular hydrogen bonds to a morin molecule. Also, the three rings of morin hydrate approach coplanarity. This conformation favours a delocalization of electrons after oxyradical reduction, making morin an effective antioxidant. Thus, we have documented some of the molecular properties and myocardial salvage effects of morin hydrate.

Molecular structure and antioxidant specificity of purpurogallin in three types of human cardiovascular cells.

Purpurogallin (PPG) in an active cytoprotector found in certain oak barks. We have shown that PPG prolongs the survival of cultured cardiocytes from rats and rabbits against different oxidants better than do antioxidants such as Trolox (a hydrophilic analogue of vitamin E) in a morphometric assay system. First, we verified by X-ray crystallography that PPG is a bicyclic molecule comprising a phenolic ring fused with a seven-membered ring in a highly planar conformation. In analogues of PPG wherein the two double bonds in the seven membered ring of the parent molecule are saturated or where the four OH groups of the parent compound are substituted by four OCH3 groups, the derivatives are less planar and less protective of the human cells than native PPG. Second, PPG in a concentration-dependent manner protected myocytes and endothelial cells of humans against oxyradicals generated with any one of the following oxyradical generators: (a) xanthine oxidase plus hypoxanthine, (b) menadione, or (c) paraquat. In each case, PPG was more cytoprotective than comparative antioxidants. Also, PPG protected erythrocytes against peroxyl radicals better than the two PPG derivatives mentioned. Third, the cytoprotective action of PPG detected in vitro was accompanied by declines of malondialdehyde. Finally, we observed that PPG chelated ferrous ions and, therefore, can suppress the formation of radicals in the Fenton reaction. Thus, PPG with its molecular architecture and presumably its affinity for ferrous ions protects multiple types of cardiovascular cells against oxyradicals.

Methylenecyclopropane Analogues of Nucleosides: Synthesis, Absolute Configuration, and Enantioselectivity of Antiviral Effect of (R)-(-)- and (S)-(+)-Synadenol

Synthesis, absolute configuration and antiviral activity of enantiomeric antiviral agents (R)-(-)- and (S)-(+)-synadenol (2 and 3a) are described.

Bis(2,2-dimethylaziridinyl)phosphinic amide

The asymmetric unit of the title compound, C8H18N3OP, contains one bis(2,2-dimethylaziridinyl)phosphinic amide molecule. The crystal structure is characterized by hydrogen bonds from the amide-N atom, which involve both H atoms of the amino group, to the phosphinic-O atom in two different molecules, thus forming infinite double-stranded chains along the base vector [100], and by hydrophobic contacts between these chains.

The antifolate trimetrexate : observation of the enzyme-binding conformation

The crystal structure of the title compound contains four 2, 4-diamino-5-methyl-6-[(3,4,5-trimethoxyanilino)methyl]quinazoline molecules, two dimethyl sulfoxide molecules and three water molecules in the asymmetric unit, i.e. 4C(19)H(23)N(5)O(3).-2C(2)H(6)OS.3H(2)O. All four quinazoline molecules adopt trans,-gauche conformations. An extensive hydrogen-bond network involving N. N base-pairing interactions, as well as the dimethyl sulfoxide and water molecules, stabilizes the crystal structure.

A Schiff base formed from sulfanilic acid and dimethylformamide

The crystal structure the Schiff base contains one 4-dimethylaminomethyleneaminobenzenesulfonic acid molecule in zwitterionic form [4-(dimethylaminomethyleneammonio)benzenesulfonate], and one water molecule in the asymmetric unit (C9H12N2O3S.H2O). Protonation occurs at nitrogen atom N1, but the charge is delocalized.

A monoamine oxidase B inhibitor: N-(2-amino­eth­yl)-p-chloro­benzamide (Ro16-6491) hydro­chloride

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved In the title compound, 2-(4-chlorobenzamido)ethanaminium chloride, C9H12ClN2O + Cl , both independent cations have linearly extended conformations, with protonation occurring at the terminal N atom. The interplanar angles between the chlorobenzoyl rings and the planar amide groups are 137.6 (3) and 149.3 (5) for cations A and B, respectively. The cations are N—H O hydrogen-bonded in a head-to-head/tail-to-tail fashion, producing distinct hydrophobic and hydrophilic layers running parallel to [110]. The Cl anions are hydrogen-bonded to the terminal positively charged –NH3 + groups. Weak C—H Cl interactions further coordinate the Cl anions. Structural comparison with pargyline, an irreversible MAO-B inhibitor, is presented.

7,8-Dihydr­oxy-4-propyl-1,2,3,4,4a,5,6,10b-octa­hydro­benzo[f]quinolinium bromide monohydrate, a dopamine agonist

In the crystal structure of the title dopaminergic compound, C16H24NO2+.Br-.H2O, protonation occurs at the piperidine N atom. The piperidine ring adopts a chair conformation and the cyclohexene ring adopts a half-chair conformation; together with the planar benzene ring, this results in a relatively planar shape for the whole molecule. Classical hydrogen bonds (N-H...Br, O-H...Br and O-H...O) produce an infinite three-dimensional network. Hydrogen bonds between water molecules and Br- anions create centrosymmetric rings throughout the crystal structure. Structural comparison of the molecule with the ergoline dopamine agonist pergolide shows that it is the hydrogen-bond-forming hydroxy or imino group that is necessary for dopaminergic activity, rather than the presence of a phenyl or a pyrrole ring per se.

2-acetamido-N-benzyl-2-(methoxyamino)acetamides: functionalized amino acid anticonvulsants.

In the crystal structure of 2-acetamido-N-benzyl-2-(methoxyamino)acetamide (3L), C12H17N3O3, the 2-acetylaminoacetamide moiety has a linearly extended conformation, with an interplanar angle between the two amide groups of 157.3 (1) degrees . In 2-acetamido-N-benzyl-2-[methoxy(methyl)amino]acetamide (3N), C13H19N3O3, the planes of the two amide groups intersect at an angle of 126.4 (4) degrees , resulting in a chain that is slightly more bent. The replacement of the methoxyamino H atom of 3L with a methyl group to form 3N and concomitant loss of hydrogen bonding results in some positional/thermal disorder in the methoxy(methyl)amino group. In both structures, in addition to classical N-H...O hydrogen bonds, there are also weak non-standard C-H...O hydrogen bonds. The hydrogen bonds and packing interactions result in planar hydrophilic and hydrophobic areas perpendicular to the c axis in 3L and parallel to the ab plane in the N-methyl derivative. Stereochemical comparisons with phenytoin have identified two O atoms and a phenyl group as molecular features likely to be responsible for the anticonvulsant activities of these compounds.