NMR assignment methods for the aromatic ring resonances of phenylalanine and tyrosine residues in proteins

The unambiguous assignment of the aromatic ring resonances in proteins has been severely hampered by the inherently poor sensitivities of the currently available methodologies developed for uniformly 13C/15N-labeled proteins. Especially, the small chemical shift differences between aromatic ring carbons and protons for phenylalanine residues in proteins have prevented the selective observation and unambiguous assignment of each signal. We have solved all of the difficulties due to the tightly coupled spin systems by preparing regio-/stereoselectively 13C/2H/15N-labeled phenylalanine (Phe) and tyrosine (Tyr) to avoid the presence of directly connected 13C-1H pairs in the aromatic rings. The superiority of the new labeling schemes for the assignment of aromatic ring signals is clearly demonstrated for a 17 kDa calcium binding protein, calmodulin.     

Total synthesis and absolute stereochemistry of pentenocin B, a novel interleukin-1 beta converting enzyme inhibitor

Four possible diastereomers of pentenocin B were synthesized in a stereocontrolled manner, and the first total synthesis of a natural enantiomer of (+)-pentenocin B unequivocally established the absolute stereochemistry to be 4S,5R,6R.     

A concise route to (+)-lactacystin

A facile chromatography-free route to Kang's intermediate for the synthesis of (+)-lactacystin, a potent proteasome inhibitor, has been developed starting with Brown's asymmetric crotylation of tert-butyl 5-formyl-2,2-dimethyl-1,3-dioxan-5-ylcarbamate, easily available from 2-amino-2-(hydroxymethyl)propane-1,3-diol (Tris).     

Kinetic Resolution of Racemic Secondary Benzylic Alcohols by the Enantioselective Esterification Using Pyridine‐3‐carboxylic Anhydride (3‐PCA) with Chiral Acyl‐Transfer Catalysts

Pyridine‐3‐carboxylic anhydride (3‐PCA) was found to function as an efficient coupling reagent for the preparation of carboxylic esters from various carboxylic acids with alcohols under mild conditions by a simple experimental procedure. This novel condensation reagent 3‐PCA was applicable not only for the synthesis of achiral carboxylic esters catalyzed by 4‐(dimethylamino)pyridine (DMAP) but also for the production of chiral carboxylic esters by the combination of chiral nucleophilic catalyst, such as tetramisole (=2,3,5,6‐tetrahydro‐6‐phenylimidazo[2,1‐b][1,3]thiazole) derivatives. An efficient kinetic resolution of racemic benzylic alcohols with achiral carboxylic acids was achieved by using 3‐PCA in the presence of (R)‐benzotetramisole ((R)‐BTM), and a variety of optically active carboxylic esters were produced with high enantiomeric excesses by this new chiral induction system without using a tertiary amine.     

1H-NMR Relaxation of Water Molecules in the Aqueous Microcrystalline Cellulose Suspension Systems and Their Viscosity

An intensive study for aqueous microcrystalline cellulose (MCC) suspensions was carried out in view of the relationship between a viscosity and a 1H spin-spin relaxation time (T2) of water. An investigation was carried out for four suspension systems with the different particle size distributions. The proton mole ratio () of bound water against MCC particles and T2 of bound water (T2,b) were evaluated from the T2 values obtained by Carr-Purcell- Meiboom-Gill (C.P.M.G) method and those by solid echo method, respectively. As a result of these analyses, the T2,b value for the aqueous MCC suspension was evaluated as 5 × 10–3 s and it was found that the system having a larger tended to show a higher viscosity. By relating the above results to the observation of the suspensions by an optical microscope, it was concluded that a network formed by MCC particles plays an important role in generating a high viscosity of MCC suspension, and that an averaged mobility of water molecules is sensitively affected by the network structure.     

Redox features of β-VOPO4 catalyst using tracer and laser Raman spectroscopy

The oxygen ions of the β-VOPO₄ catalyst were exchanged with an tracer by a reduction–oxidation method and by a catalytic oxidation of but-1-ene using ₂. The bands at 992 and 900 cm⁻¹ were more shifted to lower frequencies than those at 1076 and 1002 cm⁻¹. Applying the correlation between the Raman bands and stretching vibrations in the literature, the exchanged oxygen species were estimated. The results suggest that the P–O–V vacancies corresponding to 992 and 900 cm⁻¹ were responsible for reoxidation and the V=O oxygen corresponding to the 1002 cm⁻¹ band of β-VOPO₄ was not. The (VO)₂P₂O₇ was oxidized to β-VOPO₄ by O₂ above 823 K. The insertion position of oxygen was determined at the bands at 992 and 900 cm⁻¹ of β-VOPO₄ using ₂, which is the same as the exchanged position.     

Catalytic property of Europium supported on alumina from its ammoniacal solution

Europium supported on alumina (Eu/Al₂O₃) was prepared by impregnation from an ammoniacal solution of the metal. The catalytic activity of Eu/Al₂O₃ for the isomerization of 2,3-dimethylbut-1-ene to 2,3-dimethylbut-2-ene was examined. Eu/Al₂O₃ showed the highest catalytic activity for the isomerization when heated under a vacuum at 523 K, the yield of 2,3-dimethylbut-2-ene in 20 min being 81.6% at 314 K. IR spectrum shows the presence of two kinds of Eu amides. The change of the IR spectra and the catalytic activities with evacuation temperature suggest that only one of the two Eu amides is catalytically active for this base-catalyzed isomerization.     

Broad spectrum and mode of action of an antibiotic produced byScytonema sp. TISTR 8208 in a seaweed-type bioreactor

A photobioreactor was constructed using anchored polyurethane foam strips (1 x 1 x 40 cm) fixed onto a stainless-steel ring to prevent flotation, as a biomass support material (BSM). This type of reactor was named a seaweed-type bioreactor. A filamentous cyanobacterium, Scytonema sp. TISTR 8208, which produces a novel cyclic dodecapeptide antibiotic, was immobilized in seaweed-type photobioreactor and cultivated with air containing 5% CO₂ sparged at a gas flow rate of 250 mL/min under illumination at a light intensity of 200 μmol photon m^-2s^-1. The antibiotic produced in the seaweed-type photobioreactor was purified by HPLC and examined regarding its spectrum and mode of action. The antibiotic effectively inhibited the growth of Gram-positive bacteria, pathogenic yeasts, and filamentous fungi, but it had only a weak effect on Gram-negative bacteria. Scanning electron micrograph analysis showed that the most characteristic change was swelling of the cells after exposure to the antibiotic. The antibiotic seems to alter the conformation of the microbial cell membrane, thereby changing its permeability, leading to osmotic shock.     

Metal-metal d-d interaction through the discrete stacking of mononuclear M(II) complexes (M = Pt, Pd, and Cu) within an organic-pillared coordination cage

Two molecules of planar MII(acac)2 complexes (M = Pt, Pd, and, Cu; acac = acetylacetonato) are efficiently stacked within an organic-pillared coordination cage, exhibiting characteristic spectroscopies (for M = Pt and Pd) and electron spin-spin coupling (for M = Cu) attributable to metal-metal interaction.     

Dioxygenases, key enzymes to determine the aglycon structures of fusicoccin and brassicicene, diterpene compounds produced by fungi

Fusicoccin A and cotylenin A are structurally related diterpene glucosides and show a phytohormone-like activity. However, only cotylenin A induces the differentiation of human myeloid leukemia cells. Since the cotylenin A producer lost its ability to proliferate during preservation, a study on the relationship between structure and activity was carried out and a modified fusicoccin A with hydroxyl group at the 3-position showed a similar biological activity with that of cotylenin A. We then searched for an enzyme source that catalyzes the introduction of a hydroxyl group into the 3-position and found that brassicicene C, which is structurally related to fusicoccin A with hydroxyl group at the 3-position, was produced by Alternaria brassicicola ATCC96836. We recently cloned a brassicicene C biosynthetic gene cluster including the genes encoding fusicocca-2,10(14)-diene synthase and two cytochrome P450s, which were responsible for the formation of fusicocca-2,10(14)-diene-8β,16-diol. In this study, we report that a α-ketoglutarate dependent dioxygenase, the gene coding for which was located in the cluster, catalyzed a hydroxylation at the 3-position of fusicocca-2,10(14)-diene-8β,16-diol. On the other hand, a α-ketoglutarate-dependent dioxygenase, which had been identified in a fusicoccin A biosynthetic gene cluster, catalyzed the 16-oxidation of fusicocca-2,10(14)-diene-8β,16-diol to yield an aldehyde (8β-hydroxyfusicocca-1,10(14)-dien-16-al), although both dioxygenases had 51% amino acid sequence identity. These findings suggested that the dioxygenases played critical roles for the formation of the fusicoccin A-type and cotylenin A-/brassicicene C-type aglycons. Moreover, we showed that short-chain dehydrogenase/reductase located in the fusicoccin A biosynthetic gene cluster catalyzed the reduction of the aldehyde to yield fusicocca-1,10(14)-diene-8β,16-diol.