Shigetaka Koda

Determination of cefixime and its metabolises by high-performance capillary electrophoresis

Cefixime (CX), an oral cephalosporin antibiotic, and its metabolites in human digestive organs were separated by various modes of high-performance capillary electrophoresis. The zone electrophoresis mode in phosphate buffer (pH 6.8) containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate gave the best separation, permitting the complete resolution of CX and all of five metabolites. On the other hand, the plain zone electrophoresis mode in phosphate buffer (pH 6.8) offered a simple procedure for the direct determination of urinary CX concentration using intact urine samples.

A New Nitric Oxide (No) Releaser: Spontaneous No Release from Fk409

The remarkable vasorelaxant and anti-platelet effects of FK409 have been reported to be due to nitric oxide (NO) release. The purpose of the present study is to investigate the spontaneous NO-releasing pathway of FK409 in aqueous solutions. 1H-NMR spectra of FK409 suggested that the compound underwent a time-dependent elimination of the hydrogen atom at alpha-position of the nitro moiety (at the 5-position) in weakly alkaline solutions. In addition, the degradation of FK409 monitored by HPLC showed a pH-dependency accelerating with an increase of pH. These results revealed that the first step in the degradation of FK409 might be the hydroxyl ion-dependent subtraction of the hydrogen atom at the 5-position. On the other hand, NO release from FK409 also exhibited a pH-dependency, and the velocity of NO liberation was markedly enhanced above pH 6. Furthermore, a linear relationship between the rate of FK409 degradation and that of NO formation was observed, indicating that the rate-limiting step for NO formation is the same as that for degradation. Thus, the rate-limiting process of NO formation from FK409 is due to the deprotonation reaction of the hydrogen atom at the 5-position by hydroxyl ions. The deprotonation process appears to be an essential step for both FK409 degradation and NO release. On the basis of the results, a possible kinetic scheme for NO release from FK409 is proposed.

Dehydration effect on the stability of cefixime trihydrate

Abstract Partially dehydrated cefixime trihydrate was found to be unstable due to a highly disordered crystal structure caused by loss of its water of crystallization. It was also confirmed that cefixime trihydrate stored at a relative humidity below its critical value was less stable than the trihydrate stored under moist conditions. On the other hand, completely dehydrated cefixime trihydrate was relatively stable since it underwent transformation to a new anhydrous crystal form which did not contain water capable of participating in the hydrolytic reaction. It was suggested that the degradation mechanism under conditions of dryness differed from that under conditions of humidity, since not only the appearance but also the particular species of degradation products were completely different under the two sets of conditions.

Novel Glycosidic Linkage between Arabinogalactan and Peptidoglycan in the Cell Wall Skeleton of Nocardia rubra AN-115

A glycosidic linkage between the arabinogalactan and peptidoglycan has been demonstrated for the first time in cell walls from Nocardia rubra AN-115. Two oligosaccharides, Rha-(1→3)-GlcNAc and Gal-Rha-(1→3)-GlcNAc, were identified by gas chromatography-mass spectrometry in acid hydrolysates of arabinogalactan containing defective peptidoglycan polymer obtained from stepwise alkaline degradations of N. rubra AN-115 walls. The arabinogalactan of N. rubra AN-115 walls contained not only Ara and Gal but also Rha, while peptidoglycan contained glycan polymers composed of GlcNAc-MurNGl units. These findings strongly suggest that arabinogalactan was linked glycosidically to peptidoglycan through a Rha-GlcN Ac linkage in N. rubra AN-115 walls.

Mechanism of Optical Isomerization of(S)-N-[1-(2-Fluorophenyl)-3,4,6,7-tetrahydro-4-oxopyrrolo[3,2,1-jk] [l,4]-benzodiazepine-3-y1]-1H-indole-2-carboxamide (FK480) in Soft Capsules Containing Polyethylene Glycol 400 and Glycerol

FK480 is a new synthetic non-peptide antagonist of cholecystokinin (CCK)-A receptors. The dosage form of FK480 is a soft capsule containing a solution of FK480 in a mixture of polyethylene glycol 400 (PEG 400) and glycerol to improve its bioavailability. Studies on the stability of this FK480 dosage form revealed that the main degradation occurred by optical isomerization at the asymmetric C-3 position of the pyrrolobenzodiazepine ring. The degradation reaction was accelerated by formic acid formed in a mixture of PEG 400 and glycerol. Addition of amino acids to the capsule solution retarded the isomerization by reacting with formic acid. Therefore, formic acid appears to accelerate optical isomerization of FK480.

Structural studies of FR900359, a novel cyclic depsipeptide from Ardisia crenata sims(Myrsinaceae)

The molecular structure and absolute configuration of FR900359, a novel cyclic depsipeptide from Ardisia crenata sims, has been determined by a combination of X-ray crystallographic analysis and g.c./m.s. study of the diastereomeric derivatives of its constituents. There are five intramolecular hydrogen bonds (or short contacts) in the FR900359 molecule. All the imino nitrogen and hydroxy oxygen atoms having a proton-donating ability efficiently participate in the hydrogen bond network. The FR900359 molecule contains two cis peptide bonds, in a conformation which can take part in the hydrogen bonds. This hydrogen bond network contributes to the stabilization of the overall structure of FR900359; constituents not restrained by this network are considered to be flexible. Since the N-methyldehydro-L-alanine residue falls within the unstable region of a Ramachandran (φ–ψ) plot, it is vulnerable to nucleophilic attack and may, therefore, be involved in the biological activity of FR900359.

Nitric Oxide (NO)-releasing Pathway of FK409 in the Presence of Sulfhydryl-bearing Compounds

AbstractPurpose. We have recently reported that degradation of FK409 with generation of NO is spontaneous and is accelerated in the presence of sulfhydryl-bearing compounds, such as L-cysteine (Cys) and glutathione (GSH). The purpose of the present study is to investigate the NO-releasing pathway of FK409 in the presence of sulfhydryl-bearing compounds. Methods. The degradation process of FK409 in the presence of Cys or GSH was investigated by means of 1H-nuclear magnetic resonance (NMR) spectroscopy and high-performance liquid chromatography (HPLC). Results. The degradation of FK409 in the presence of Cys was dependent on concentration of Cys, and showed pH-dependency, accelerating with an increase in pH. The 1H-NMR spectra of FK409 with Cys suggested that time-dependent elimination of the hydrogen atom at the α-position of the nitro moiety (5-position) was accelerated by Cys in weakly alkaline solution. Cys and GSH were transformed readily, concomitant with FK409 degradation, to give their oxidized forms and probably S-nitrosothiols. Conclusions. The effect of sulfhydryl-bearing compounds on FK409 degradation is due to the acceleration of deprotonation of the hydrogen atom at the 5-position by thiolate anion as well as hydroxyl ion. Sulfhydryl-bearing compounds reacted with the released NO resulting in formation of disulfides via intermediate S-nitrosothiols.

Antitumour Activity of Purified Arabinogalactan-peptidoglycan Complex of the Cell Wall Skeleton of Rhodococcus lentifragmentus

Antitumour activity of arabinogalactan peptidoglycan (AP) complex (peptidoglycan and arabinogalactan liberated by an acid or alkaline treatment from Rhodococcus lentifragmentus AN-115 cell wall skeleton) was examined in mice and compared with that of the cell wall skeleton. The growth of syngeneic fibrosarcoma Meth A cells after implantation in BALB/c mice was significantly suppressed by AP complex, and also regressed after intratumoral injection of AP complex on days 1, 4 and 7 after tumour implantation. Although the activity of peptidoglycan was less than that of AP complex, peptidoglycan also showed both tumour-suppressive and regressive activities. Arabinogalactan did not show antitumour activity. It is interesting that peptidoglycan has an important role in the effect against tumours.

moisture adsorption-desorption effect on the structure of inclusion complex of 6-chloro-2-pyridylmethyl nitrate and β-cyclodextrin

Abstract— A new anti‐anginal drug, 6‐chloro‐2‐pyridylmethyl nitrate (FR46171), was found to form a complex with β‐cyclodextrin (β‐CyD), molecular ratio 1:1. The FR46171/β‐CyD complex thus prepared showed a moisture adsorption‐desorption hysteresis characteristic of hydrophilic polymers. The moisture adsorption‐desorption isotherm and differential scanning calorimetry indicated that the moisture adsorbed FR46171/β‐CyD complex includes 13–15 mol of water while the moisture desorbed complex includes 5 mol of water. X‐ray diffraction patterns of these samples confirmed their different structures. The scanning electron photomicrographs and the surface areas (BET) suggested that the moisture adsorption‐desorption hysteresis observed in FR46171/β‐CyD complex can be attributed to reversible hydrogen bonding between water molecules and hydroxyl groups.

Structural Analysis of Mycolic Acids from the Cell Wall Skeleton of Rhodococcus lentifragmentus AN-115

Summary: The structures of the mycolic acids from the cell wall skeleton of Rhodococcus lentifragmentus AN-115 were established. Field desorption mass spectrometry of underivatized mycolic acids showed that the molecular species of the mycolic acids were distributed from C38 to C50 and the major components were C44, C46 and C48 mono- and dienoic β-hydroxy fatty acids. Pyrolysis gas chromatography-mass spectrometry confirmed that the mycolic acids consisted of a saturated straight C12 and C14 α-chain and an unsaturated β-chain, having mainly C29 and C31 carbons with one or two double bonds. The double bonds in the β-chain were established as the cis isomers by nuclear magnetic resonance. The absolute configurations of the α- and β-asymmetric carbons were both established as R using molecular rotation data.