Determination of the Rates of Formation and Hydrolysis of the Schiff Bases Formed by Pyridoxal 5′-Phosphate with Copolypeptides Containing L-Lysine and Aromatic L-Amino Acids

The apparent rate constants of formation (k₁) and hydrolysis (k₂) of the Schiff bases formed between pyridoxal 5′-phosphate and the poly(L -Lys,L -Trp)4 : 1 copolymer at different pH values, a temperature of 25 °C and an ionic strength of 0.1 M were determined. The individual rate constants of formation and hydrolysis of the Schiff bases of pyridoxal 5′-phosphate with poly(L -Lys,L -Trp)4 : 1, poly(L -Lys,L -Tyr)4 : 1, and poly(L -Lys,L -Phe)1 : 1 corresponding to the different chemical species present in the medium as a function of its acidity were also determined, as were the pK values for the Schiff bases. The significance of the interactions between the pyridine ring in pyridoxal 5′-phosphate and the aromatic ring in the L -phenylalanine, L -tyrosine, and L -tryptophan side chains is demonstrated.     

Kinetic Study on Stability of Schiff Base of Pyridoxal 5′-Phosphate and Leucine in Water Media with Cationic Surfactants

We studied the stability of the Schiff bases formed between pyridoxal 5′-phosphate (PLP) and leucine in the presence of (hexadecyl)trimethylammonium bromide (CTAB) over a wide pH range by determining the kinetic constants of formation and hydrolysis of these compounds. The results show that the stability of the Schiff bases is increased by the presence of CTAB as a result of increased rates of formation and decreased hydrolysis rate constants. The ionic head groups of CTAB favour the formation of the bases, while its hydrophobic rests protect the imine double bond from hydrolysis. This model system permits one to obtain partially hydrophobic media with no need for any non-aqueous solvents.     

Complexation Properties of Schiff Bases Containing the N-Phenylaza-15-crown-5 Moiety

The complexation of a series of new Schiff bases containing theN-phenylaza-15-crown-5 (Ph-A15C5) moiety with alkali and alkaline-earth metal ions (incl. Be²⁺ and Mg²⁺, is studied by means of UV-Vis spectroscopy. The corresponding stability constant values are determined and discussed from two aspects: the position of the Ph-A15C5 moiety in the ligand molecule and the nature of the metal ion.     

含有三苯胺环类席夫碱的合成

以4,4’-二甲酰基三苯胺为原料,通过Wittig和胺醛缩合反应合成了两个含有三苯胺环席夫碱类化合物——4-(对甲基苯乙烯基)-4’-亚(α-萘胺)甲基三苯胺和4-(对甲基苯乙烯基)-4’-亚(2-氨基芴)甲基三苯胺,其结构经1H NMR,13CNMR和IR确证。     

Synthesis of 2′-Deoxyisoguanosine 5′-Triphosphate and 2′-Deoxy-5-methylisocytidine 5′-Triphosphate

The syntheses of the 5′-triphosphates of 2′-deoxyisoguanosine (=p₃isoG_d) and 2′-deoxy-5-methylisocytidine (=p₃me⁵isoC_d), two new bases for the genetic alphabet, are described. The triphosphates were synthesized from the corresponding nucleosides using a transient-protection procedure. The introduction of a methyl group at the 5-position of 2′-deoxyisocytidine remarkably improved the stability of the triphosphate. Characterization of the triphosphates included enzymatic incorporation opposite the complementary base in a template oligonucleotide.     

Oligodeoxynucleotide Duplexes Containing (5′S)‐5′‐C‐Alkyl‐Modified 2′‐Deoxynucleosides: Can an Alkyl Zipper across the DNA Minor‐Groove Enhance Duplex Stability?

A series of oligonucleotides containing (5′S)‐5′‐C‐butyl‐ and (5′S)‐5′‐C‐isopentyl‐substituted 2′‐deoxyribonucleosides were designed, prepared, and characterized with the intention to explore alkyl‐zipper formation between opposing alkyl chains across the minor groove of oligonucleotide duplexes as a means to modulate DNA‐duplex stability. From four possible arrangements of the alkyl groups that differ in the density of packing of the alkyl chains across the minor groove, three (duplex types I – III , Fig. 2) could experimentally be realized and their duplex‐forming properties analyzed by UV‐melting curves, CD spectroscopy, and isothermal titration calorimetry (ITC), as well as by molecular modeling. The results show that all arrangements of alkyl residues within the minor groove of DNA are thermally destabilizing by 1.5–3°/modification in T_m. We found that, within the proposed duplexes with more loosely packed alkyl groups (type‐ III duplexes), accommodation of alkyl residues without extended distorsion of the helical parameters of B‐DNA is possible but does not lead to higher thermodynamic stability. The more densely packed and more unevenly distributed arrangement (type‐ II duplexes) seems to suffer from ecliptic positioning of opposite alkyl groups, which might account for a systematic negative contribution to stability due to steric interactions. The decreased stability in the type‐ III duplexes described here may be due either to missing hydrophobic interactions of the alkyl groups (not bulky enough to make close contacts), or to an overcompensation of favorable alkyl‐zipper formation presumably by loss of structured H₂O in the minor groove.     

一类新型含噻吩环西夫碱的合成

通过4，4，4-三氟-1-(2-噻吩基)-1，3-丁二酮与一系列氨基化合物缩合合成了一类新型含噻吩环的西夫碱。其组成与结构经元素分析，IR，1HRNMR和MS进行了表征。     

Synthesis of various 5-substituted 2′-deoxy-3′-5′-di-O-acetyluridines

The Pd(0)-catalyzed coupling reaction of β-5-iodo-2′-deoxy-3′,5′-di-O-acetyluridine with various heteroaryltrimethylstannyl compounds gave the corresponding β-5-heteroaryl-2′-deoxy-3′,5′-di-O-acetyluridines in moderate yields. This direct coupling approach for nucleosides represented an interesting alternative to the 5-heteroaryl functionalization of pyrimidines followed by the Hilbert-Johnson glycosylation reaction which often yields mixtures of the α and β anomers.     

3′,4′-Diethynl-2′,3′,5′-trideoxy-5′-noruridine: A new self-polymerizable 2′-deoxyribonucleoside analogue

In 10 steps, 3′,4′-diethynyl-2′,3′,5′-trideoxy-5′-noruridine ( 14 ) was synthesized in 5% overall yield from commercial uridine, using conventional methods of nucleoside chemistry. As two functional groups capable to react with each other are present in the same molecule, the synthetic compound is able to form polymers, similar to the polynucleotides, by an acetylene coupling reaction.     

Photophysical Study of Pyridoxal 5'-Phosphate and Its Schiff Base with n-Hexylamine

Abstract— Phosphopyridoxal enzymes exhibit a wide variety of reactions. The activation mechanism proceeds with the formation of Schiff bases that undergo loss or transfer of one or more protons. Changes in the fluorescent properties of the pyridoxal 5'-phosphate and its Schiff base may signal changes in the protonation state and/or in the microenvironment of the cofactor. In this paper the average fluorescence lifetime of pyridoxal 5'-phosphate (PLP) as a function of pH was studied in a medium of 0.1 M ionic strength at 25°C. The ionic species of PLP with an unprotonated hydrogen atom were found to exhibit fluorescence lifetimes in the region of 100 ps on excitation at λ= 390 nm. The average fluorescence lifetimes for PLP in its Schiff bases with n-hexylamine in media of low polarity are reported.     

Synthesis of New Schiff Bases and Polycyclic Fused Thiopyranothiazoles Containing 4,6‐Dichloro‐1,3,5‐Triazine Moiety

New aromatic aldimines, isatine substituted ketimines based on (4,6‐dichloro‐1,3,5‐triazin‐2‐yl)‐hydrazine scaffold and polycyclic fused thiopyranothiazoles formed using hetero‐Diels‐Alder reactions starting from 4‐thioxo‐2‐thiazolidinones and 5‐norbornene‐2,3‐dicarboxylic acid triazino‐derivatives synthetic approach is described. The application of condensation and cyclocondensation reactions of N‐nucleophiles and carbonyl agents for synthesis a number of biologically active triazine derivatives is reported. Screening of anticancer activity in vitro yielded the most active compounds 3a , 8b , and 8f for different cell lines.     

Schiff bases between pyridoxal 5′-phosphate and dodecylamine. Kinetic study

We studied the formation and hydrolysis of the Schiff base of pyridoxal-5′ -phosphate (PLP) and n-dodecylamine (DOD) by kinetic methods and found the formation rate constants to be much larger than those reported for related systems. This can be ascribed to the occurrence of local concentration of charges in the vicinity of the carbinolamine, which stabilizes the corresponding transition state of the dehydration reaction. On the other hand, the hydrolysis rate constants of our system were considerably smaller as a result of the 12-atom hydrocarbon chain acting as a bulky hydrophobic rest protecting the imine bond from attack by water.     

含硫Schiff碱的合成及其抑菌活性

1-苯基-3-甲基-4-苯甲酰基-5-吡唑啉酮分别与氨基硫脲、肼基二硫代甲酸苄酯、肼基二硫代甲酸甲酯和1,3-二氨基硫脲反应合成了6个含硫Schiff碱(6a~6 e),其结构经UV,1H NMR,IR和元素分析表征。初步生物活性测试结果表明,部分6对大肠杆菌和枯草芽孢杆菌具有一定的抑菌活性。