So-Yeop Han

Monoacetyldiglycerides as new Ca2+ mobilizing agents in rat pancreatic acinar cells

Several monoacetyldiglycerides were synthesized from glycerol in search for new Ca2+ mobilizing agent in vitro. All monoacetyldiglycerides except linolenoyl and phenlycyclopropylcarbonyl derivatives showed activity toward Ca2+ release in pancreatic acinar cells. Linoleoyl and docosahexaenoyl derivatives were chosen for further test and exhibited unique activity.

An efficient synthesis of 2,5-diketopiperazine derivatives by the Ugi four-center three-component reaction

A facile synthetic approach to 2,5-diketopiperazines 4 by the Ugi four-center three-component reaction using commercially available dipeptides as a bifunctional component, aldehydes, and isocyanides was described.

Studies toward a synthesis of C3-epimauritine D: construction of the macrocycle

We successfully synthesized a 14-membered cyclic enamide of C3-epimauritine D from the cis-2,3-pyrrolidinediol derivative. Treatment of the pyrrolidinediol with nitrobenzonitrile in an SNAr reaction efficiently installed the desired aryl–alkyl ether linkage on the N-heterocyclic system. Macrocyclization was successfully achieved by the use of TFFH as the peptide coupling reagent in the presence of HOAt.

Spectroscopic, crystallographic and computational studies of the formation and isomerization of cyclic acetals and ketals of pentonolactones ☆

Abstract The different reactivities of D-ribonolactone, L-arabinonolactone, D-xylonolactone, D-lyxonolactone 2-deoxy-D-ribonolactone toward benzaldehyde and acetone in acidic media, were examined. The reactions involved complex equilibria and were investigated with extensive 13C NMR studies as well as X-ray crystallographic analysis of selected products. Molecular mechanics (MM2) and semiempirical (PM3 and AM1) calculations of some derivatives were carried out in order to facilitate structural and conformational assignments. The differences in reactivity observed for the reactions of D-pentono-1,4-lactones with benzaldehyde and acetone are rationalized in terms of their structural and conformational features.

Synthesis of 1-lyso-2-palmitoyl-rac-glycero-3-phosphocholine and its regioisomers and structural elucidation by NMR spectroscopy and FAB tandem mass spectrometry

Abstract Three regioisomers of a naturally occurring lysophosphatidylcholine were chemically synthesized from glycerol. The phosphocholine moiety of the molecule was introduced by sequentially reacting with ethylene chlorophosphite, bromine, water, and trimethyl amine. Removal of a silyl protecting group of the hydroxyl group in the glycerol backbone was achieved without any accompanying acyl migration in the final stage of the synthesis by using NBS in a dimethyl sulfoxide–water cosolvent system. Structures of all regioisomers were compared by NMR spectroscopy and FAB tandem mass spectrometry.

Identification of triacylglycerols containing two short-chain fatty acids at sn-2 and sn-3 positions from bovine udder by fast atom bombardment tandem mass spectrometry

Several triacylglycerol (TAG) molecular species, that contain two short-chain fatty acids (C4 to C8) at the sn-2 and sn-3 positions of the glycerol backbone, were isolated from bovine udder by using solvent extraction and silica gel column chromatography. Their structures were identified by fast atom bombardment (FAB) tandem mass spectrometry (MS/MS), based on the information obtained from collision-induced dissociation (CID) spectra of sodium-adducted molecules ([M + Na](+)) of model TAG compounds which had been synthesized from glycerol and appropriate fatty acids. For each species, the relative positions of the three fatty acids on the glycerol backbone, as well as fatty acid composition and double-bond position in the fatty acyl group, were determined. A majority of sodium-adducted molecules observed in the FAB mass spectrum were mixtures of at least two components that have different fatty acid composition but the same molecular mass. In addition, all the components present in mixtures of all the species contain a long-chain fatty acid (C12 to C18) at the sn-1 position, a short-chain fatty acid (C4 to C8) at the sn-2 position, and a butyric acid uniquely at the sn-3 position.

Investigations of the formation of cyclic acetal and ketal derivatives of D-ribono-1,4-lactone and 2-deoxy-D-ribono-1,4-lactone

The reactions of D-ribono-1,4-lactone, and 2-deoxy-D-ribono-1,4-lactone with benzaldehyde and acetone in acidic media were investigated. The products obtained were isolated and characterized. The 1H NMR spectra of the 1,5-lactone product resulting from the thermodynamically controlled reaction of D-ribono-1,4-lactone with benzaldehyde were examined between 300 °K and 200 °K in a polar solvent. No conformational changes in the 1,5-lactone ring were observed within this temperature range. Detailed NMR studies showed that the acetalization of D-ribono-1,4-lactone proceeded with the initial formation of the endo-2,3-acetal derivative, which in the presence of aqueous acids underwent ring expansion and isomerization to the 3,4-acetal of the 1,5-lactone. The endo preference of benzylidene acetals was explained by the transition state conformation of the reactants and the thermodynamic stability of the products, as calculated with molecular mechanics.

Lysophosphatidylcholine derived from deer antler extract suppresses hyphal transition in Candida albicans through MAP kinase pathway.

A family of 2-lysophosphatidylcholines (lyso-PCs) was isolated from deer antler extract, guided exclusively by hyphal transition inhibitory activity in Candida albicans. Structural determination of the isolated lyso-PCs by spectroscopic methods, including infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR, 2D correlation spectroscopy NMR, fast atom bombardment mass spectrometry and tandem mass spectrometry, confirmed that the natural products were composed of at least four different lyso-PCs varying in fatty acid moiety at the sn-1 position of the glycerol backbone. The major lyso-PCs were confirmed as 1-stearoyl-, 1-oleoyl-, 1-linoleoyl- and 1-palmitoyl-2-lyso-sn-glycero-3-phosphatidylcholines. Lyso-PC specifically suppressed the morphogenic transition from yeast to hyphae in C. albicans, without affecting the growth of either yeast or hyphae. Lyso-PC exerted hyphal transition that suppressed activity in the broad spectrum of the Candida species, such as C. albicans, Candida krusei, Candida guilliermondii and Candida parapsilosis. Northern analysis indicated that the suppression was mediated through the mitogen-activated protein kinase pathway.

ANALYSIS OF A MACH-ZEHNDER INTERFEROMETRY MEASUREMENT OF THE POCKELS COEFFICIENTS IN A POLED POLYMER FILM WITH A REFLECTION CONFIGURATION

Mach-Zehnder interferometry is employed to measure the Pockels coefficients in a poled thin polymer film, which serves as a reflection mirror in the sample arm of the interferometer. As a complete optical characterization of the electro-optic polymer film, the modulated light intensity of the Mach-Zehnder interferometer is investigated as a function of the optical bias in the reference arm, the modulation voltage applied to the film, the polarization angle of the incident light, and the angle of incidence on the film. The Mach-Zehnder interferometry measurement of the Pockels coefficients in the reflection configuration has an advantage over single-beam polarization interferometry in permitting the independent determination of the Pockels tensor components, r13 and r33. Particularly, in a reflection configuration two-beam interferometric measurement, a proper consideration of the optical path change due to the refractive angle change is found to be critical in determining the absolute values of the Pockel...

The detoxin complex: a naturally occurring safener

The detoxin complex is a group of depsipeptide metabolites produced by the organism Streptomyces caespitosus var. detoxicus 7072 GC 1 as well as other strains of streptomyces. The complex is the first isolated natural product which displays a unique detoxification effect in plant and animal cells as its biological activity. The structural investigations carried out to elucidate the structures of the congeners and the stereochemistry of the stereogenic centers are described. Structure-activity relationships are discussed. The different synthetic approaches to the parent amino acid, (-)detoxinine, are compared. The syntheses of detoxins (-)-B 1 , (-)-B 3 , (-)-D 1 , and (+)-valyldetoxinine are described