Microbial degradation of physiologically active peptides by strain B-9

The reaction of some physiologically active peptides with bacterial strain B-9 has been investigated. Bradykinin, β-endorphin, and [Leu(5)]enkephalin were quickly degraded, with half-lives of <5 min. Somatostatin, substance P, and angiotensin I were degraded relatively smoothly, with half-lives of 10 min to 1 h, whereas oxytocin and insulin were slowly degraded, with half-lives of 1 and 4 days, respectively. Vasopressin was barely degraded, with a half-life of >7 days. Linearized vasopressin, prepared by the reductive cleavage of the disulfide bond followed by alkylation with iodoacetamide, was degraded significantly faster than intact vasopressin, with a half-life of 2.5 h. A loop formed by disulfide bond formation was regarded as one of the degradation-resistant factors. Hydrolysis of the peptides in this study took place through cleavage of various peptide bonds, and the strain B-9 may bear similarities to the neutral endopeptidase in terms of its broad selectivity.     

Abnormal behavior of nitropyridines in substitution reactions with anions

The reactions of the anions of isonicotinamide and 2-amino-5-nitropyridine with 2-chloro-5-nitropyridine and 3-nitropyridine were observed to give rise to unexpected substitution products presumably via a radical anion mechanism.     

Time resolved photoluminescence near the “band gap” in amorphous silicon

Two broad luminescence bands in weakly hydrogenated (glow discharge) undoped amorphous silicon have been observed using time resolved spectroscopy on a nanosecond timescale. Whereas the luminescence decay of the low energy band has been found to be sample independent, the peak position of the luminescence does show a sample dependence. We propose an intrinsic origin of this luminescence.     

Synthesis of spiropolymers by polycycloaddition of ketene dimer with dinitrile oxides

Novel spiropolymers containing biisoxazolinic units in the main chain were synthesized by polycycloaddition of ketene dimer with dinitrile oxides. Ketene dimer functioned as a difunctional monomer with loss of carbon dioxide, but use of 10% excess amount seemed to be the optimum condition in terms of viscosity of the resulting polymers. These spirocyclic polymers were white to pale yellow and had inherent viscosity of up to 0.34 dl/g. Thermogravimetric analysis of the polymers showed unusual abrupt reduction of weight at 279 or 298°C. Solubility was also studied.     

A versatile route to 3-benzoheteroepines containing group 15 and 16 heavier elements involving several novel ring systems, and their thermal stabilities

The C-unsubstituted 3-benzoheteroepines (2a-g) containing group 15 (P, As, Sb, and Bi) and group 16 (S, Se, and Te) heavier elements were prepared by the reaction of the corresponding metal reagents with (Z,Z)-o-bis(beta-lithiovinyl)benzene (5) which was derived in two steps from a common o-phthalaldehyde (3). The heteroepines (2) thus obtained were thermally labile towards heteroatom extrusion, and their half-lives on heating estimated from (1)H-NMR spectral analysis showed that the 3-benzoheteroepines (2) were far less stable than the corresponding 1-benzoheteroepines (1). The 2,4-bis(trimethylsilyl)-3-benzoheteroepines (17) containing Sb, Bi, and Te were also prepared from o-diiodobenzene (9) in 6 steps and were found to be more stable than the corresponding C-unsubstituted heteroepines (2).     

O-(N-succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate-N-hydroxysuccinimide-CuCl2: a facile and reliable system for racemization-free coupling of peptides having a carboxy-terminal N-methylamino acid

Simultaneous use of N-hydroxysuccinimide (HOSu) and CuCl2 with a HOSu-based uronium coupling reagent, O-(N-succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate, has been found to eliminate the racemization of the carboxy-terminal N-methylamino acid residue during the segment condensation.     

Reactivity characteristics of squid β-chitin as compared with those of shrimp chitin: High potentials of squid chitin as a starting material for facile chemical modifications

Chemical reactivity of β-chitin isolated from squid pens has been examined in various reactions to elucidate the possibility of facile modifications in simple manners leading to the preparation of derivatives with well-defined structures. β-Chitin swelled in common solvents such as methanol and pyridine unlike the ordinary α-chitin and exhibited much higher reactivity than β-chitin. Free amino groups present in β-chitin were easily and selectively acetylated with acetic anhydride in methanol to give chitin with a uniform structure, poly(N-acetyl-D-glucosamine). When acetylation reaction was carried out in pyridine, O-acetylation proceeded smoothly besides N-acetylation. In the presence of 4-dimethylaminopyridine as the catalyst, even full acetylation was achieved under mild conditions. Tosylation was also quite efficient in pyridine without side reactions such as N-deacetylation which is unavoidable in the tosylation of α-chitin. β-Chitin also enabled direct tritylation in pyridine in the presence of 4-dimethylaminopyridine. All these reactions were quite sluggish with β-chitin, and no reactions or only very low extents of substitution were observed, indicating the high potential of β-chitin as a versatile starting material for facile modification reactions. © 1994 John Wiley & Sons, Inc.