The syntheses of tricyclic analogues of O6-methylguanine

The syntheses of the novel pyrrolo[2,3-d]pyrimidine-based heterocycles as tricyclic analogues of O6-methylguanine are described. Compound 5 is a weak inhibitor of human O6-alkylguanine DNA alkyltransferase.     

Effect of O6-methylguanine on the stability of G-quadruplex DNA

The effects of substitution of O6-methylguanine on the structure and stability of a human telomere quadruplex was studied by circular dichroism, thermal denaturation, analytical ultracentrifugation, and molecular dynamics simulations. The results show that, while quadruplex structures can form containing the modified base, they are much less stable than the normal unmodified structure. The extent of destabilization is critically dependent on the exact position of the modified base within the quadruplex structure.     

Chemical control of the photochromic reactivity of diarylethene derivatives

Photochemically inactive diarylethene derivatives having a N-(O-hydroxyphenyl) group underwent photochromic reaction when they were esterified by the addition of acetic anhydride.     

高效毛细管区带电泳法测定O~6-甲基鸟嘌呤

 建立了测定 O6-甲基鸟嘌呤浓度的高效毛细管区带电泳法。该方法以 p H9.0的硼砂为缓冲液 ,具有良好的重现性及线性关系 ,日内和日间变异系数分别为 1 .5 1 %和 1 .93 % ,平均回收率为 98.2 % ,相关系数为0 .9987,是一种简便、快速、准确、进样量少、灵敏度高的测定 O6-甲基鸟嘌呤的方法。     

Chemical modification of fumagillin. II. 6-Amino-6-deoxyfumagillol and its derivatives.

6-Amino-6-deoxyfumagillol (5) was synthesized by reductive amination of 6-oxo-6-deoxyfumagillol (4), which was obtained by oxidation of fumagillol (2). The reduction proceeded stereoselectively by the equatorial attack of hydride and 5 was found to have the same stereochemistry as that of 2. Several derivatives of 5 were prepared and most of them showed anti-angiogenic activity comparable to that of fumagillol derivatives.     

Chemical modification of plant alkaloids. 6. T-reactions of anabasine derivatives

T-reactions of anabasine derivatives were performed for the first time. Condensation of 5-nitro-2-[2-(3pyridyl)piperidino]benzaldehyde with 1,3-dimethylbarbituric acid formed an annelated tetrahydroquinoline system containing a spiropyrimidine moiety as the T-reaction product. Condensation of this same aldehyde with Meldrum’s acid was accompanied by recyclization that led to opening of the piperidine ring and closing of the tetrahydroquinolone system. A third version of the T-reaction that also led to opening of the piperidine ring but without recyclization was the condensation with dimedone.     

Methylation of pyrimidine derivatives

A mixture of isomers that differ with respect to the position of the methyl group is formed in the methylation of 5,5-diethyl-6-imino-5,6-dihydro[1H, 3H]pyrimidine-2,4-dione with excess methyl iodide in the presence of ethoxide. Isomerization of the Dimroth-rearrangement type was observed. The mass spectra of the isomers are examined, and the IR spectra of the tautomeric forms are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 823–826, June, 1978.     

Unusual deoxygenation and reactivity studies related to O6-(benzotriazol-1-yl)inosine derivatives

New and unusual developments related to the chemistry of O6-(benzotriazol-1-yl)inosine derivatives are reported. First, a simple, scalable method for their syntheses via the use of PPh3/I2/HOBt has been developed and has been mechanistically investigated by 31P(1H) NMR. Studies were then conducted into a unique oxygen transfer reaction between O6-(benzotriazol-1-yl)inosine nucleosides and bis(pinacolato)diboron (pinB-Bpin) leading to the formation of C-6 (benzotriazol-1-yl)purine nucleoside derivatives and pinB-O-Bpin. This reaction has been investigated by 11B(1H) NMR and compared to pinB-O-Bpin obtained by oxidation of pinB-Bpin. The structures of the C-6 (benzotriazol-1-yl)purine nucleosides have been unequivocally established via Pd-mediated C-N bond formation between bromo purine nucleosides and 1H-benzotriazole. Finally, short and extremely simple synthesis of 1,N6-ethano- and 1,N6-propano-2'-deoxyadenosine are reported in order to demonstrate the synthetic versatility of the O6-(benzotriazol-1-yl)inosine nucleoside derivatives for the assembly of relatively complex compounds.     

Synthesis of vitamin B6 derivatives I. Preparation of some isopyridoxamine derivatives from isopyridoxal

Improved syntheses of isopyridoxal and isopyridoxamine are described. New 5-N-substituted isopyridoxamine derivatives resulting from condensation followed by reduction of the carbonyl group of isopropylideneisopyridoxal with aniline, 2-aminothiazole and benzylamine are also reported.     

Chemical modification of plant alkaloids. I. Aminomethylation of barbituric acid derivatives by cytisine

Reaction of cytisine with 1-mono- and 1,3-disubstituted 5-arylmethylbarbituric acids in the presence of formaldehyde results in aminomethylation of C-5 to form the corresponding 5-cytisylmethylbarbituric acids. The structures of the products are found using PMR spectroscopy and mass spectrometry. 1-Phenyl-5-(2,4-dimethoxybenzyl)-5-cytisylmethylbarbituric acid is obtained as a mixture of two steroisomers in an approximately 21 ratio.I. I. Mechnikov St. Petersburg State Medical Academy, 195067, St. Petersburg, Piskarevskii pr., 47; 2) ZAO Interbioscreen, 142432, Chernogolovka, Moscow District, Institutskii pr. 8. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 152–156, March–April, 2000.     

The synthesis and chemical reactivity of 6-selenoguanosine and certain related derivatives

The synthesis of 6-selenoguanosine ( 2 ) has been accomplished by a nucleophilic displacement of the chloro group from 2-amino-6-chloro-9-(β- D -ribofuranosyl)purine ( 1 ) with either selenourea or sodium hydrogen selenide. Treatment of 2 with Raney nickel has revealed that the seleno group can be removed much easier under these conditions than the corresponding mercapto group. Alkylation of 2 with several alkylating agents occurred at the exocyclic 6-seleno group to furnish several 6-alkylseleno-2-amino-9-(β- D -ribofuranosyl)purines. Nucleophilic displacement of the 6-benzylseleno group from 2-amino-6-benzylseleno-9-(β- D -ribofuranosyl)purine ( 3c ) with sodium methoxide has been observed to occur at a faster rate than that observed for the corresponding 6-benzylmercapto derivative. A study on the relative stability between 2 and 6-seleno-9-(β- D -ribofuranosyl)purine toward basic conditions has revealed that the amino group at position two imparts an increase in stability.     

Catechol reactivity: Synthesis of dopamine derivatives substituted at the 6-position

Dopamine is a ubiquitous neurotransmitter essential in the proper functioning of the human body. In addition to this critical role, the catecholamine core has shown utility as a scaffold for numerous drugs and in other applications, like metal detection and adhesive materials. Substituents at the 6-position of dopamine’s catechol core can modulate its stereoelectronic properties, the acidity of its phenolic hydroxyl groups, and the overall hydrophobicity of the molecule. Herein, we report the synthesis of a series of four novel dopamine analogues substituted at the 6-position of catechol core. The ¹H NMR chemical shift of the aromatic proton meta to the substituent correlated strongly with the Hammett σ_m constant, confirming the electronic properties of substituents.     

Über Erdalkalioxoargentate. I. Strontiumargentat SrAg6O4

On Alkaline Earth Oxoargentates. I. Strontiumargentate SrAg₆O₄ Single crystals of SrAg₆O₄ were prepared at 400–500°C and 4000 atm. O₂-pressure. The X-ray investigation of the single crystals shows the orthorhombic space group D–Pnna (a = 6.518, b = 12.416, c = 8.909 Å). Sr²⁺ is octahedral and most of the Ag⁺ surrounded by weakly angled dumbbells of oxygen. In addition of these configurations metallic regions were found.     

The syntheses and properties of tricyclic pyrrolo[2,3-d]pyrimidine analogues of S6-methylthioguanine and O6-methylguanine

The syntheses of novel tricyclic pyrrolo[2,3-d]pyrimidine analogues of S6-methylthioguanine are described. The crystal structures and pKa values of these and related O6-methylguanine analogues are reported. All compounds display higher pKa values than O6-methylguanine with the sulfur-containing analogues being the more basic and exhibiting higher stability in aqueous solution. In a standard substrate assay with the human repair protein O6-methylguanine-DNA methyltransferase (MGMT) only the oxygen-containing analogue displayed activity.     

Interaction of the mutagenic base analogs O6-methylguanine and N4-hydroxycytosine with potentially complementary bases

Infrared spectroscopy has been employed to study possible base pair interactions, in nonpolar media, between O⁶-methylguanine and uracil, cytosine and adenine; and between derivatives of N⁴-hydroxycytosine and adenine. The association constants of O⁶-methylguanine with uracil, cytosine, and adenine are well below 1M^–1, whereas those for interaction of 1-methyl-N⁴-methoxycytosine and its 5-methyl derivative with adenine are identical, K = 14M^–1. The significance of the latter finding is discussed in relation to the conformation of the exocyclic N⁴-methoxy group. Quantum chemical calculations, with the aid of the perturbation method, were carried out for the interaction of O⁶-methylguanine with uracil, cytosine, and adenine, to establish the most energetically favoured configurations for interactions of the free bases, and of the same base pairs in the B form of DNA. The role of the conformation of the exocyclic —OCH₃ group in O⁶-methylguanine is discussed. The relevance of both the experimental and theoretical results to mutagenesis by O⁶-methylguanine and N⁴-hydroxycytosine is examined.     

Chemical modification of fumagillin. I. 6-O-acyl, 6-O-sulfonyl, 6-O-alkyl, and 6-O-(N-substituted-carbamoyl)fumagillols.

The hydroxy group of fumagillol (3), a degradation product of fumagillin (1), was acylated, sulfonylated, alkylated or carbamoylated, and the anti-angiogenic activity of the resulting products was examined. These compounds inhibited the angiogenesis induced by basic fibroblast growth factor in the rat corneal micropocket assay and the growth of vascular endothelial cells in vitro. Among them, compound 2 (AGM-1470) was found to show the most potent inhibitory effect on the growth of vascular endothelial cells and was selected from this series as a candidate for further development.     

An ab initio study of S(N)2 reactivity at C6 in hexopyranose derivatives. I. Influence of dipole-dipole interactions in the transition structure

It is widely accepted that dipole-dipole interactions in the S(N)2 transition structure can play a dominant role in determining reaction rates. A model of this type was proposed some years ago to explain the remarkably low reactivity of galactopyranose-6-O-sulfonates toward S(N)2 displacement, and similar arguments have recently been restated in the context of gas-phase reactions. In this paper, we present ab initio calculations (B3LYP/6-31+G(d,p)) on model structures and an analysis of charge densities using the theory of atoms in molecules. We find that the maximum possible impact of local dipole-dipole interactions is insufficient to account for the observed reactivity differences.