N－N－二甲基甲酰胺缩二甲醇对喋呤的甲基化反应

用N，N-二甲基甲酰胺缩二甲醇[（CH3）2NCH(OCH3)2，1]和蝶呤（2-氨基-4- 羟基蝶啶）衍生物在极性有机溶剂中反应一般得到脒化产物：N^2-(N，N-二甲基氨 基亚甲基)-蝶呤衍生物，但是在1，4-二氧六环中进行以上反应时发现，N，N-二甲 基酰胺缩二甲醇（1）不仅是脒化试剂，而且也是蝶呤化合物的甲基化试剂，并且 也依据蝶呤的N^2-位的不同取代基进行选择性的N(3)-或O^4-甲基化反应。     

Unraveling the Degradation Mechanism of Purine Nucleotides Photosensitized by Pterins: The Role of Charge‐Transfer Steps

Photosensitized reactions contribute to the development of skin cancer and are used in many applications. Photosensitizers can act through different mechanisms. It is currently accepted that if the photosensitizer generates singlet molecular oxygen (¹O₂) upon irradiation, the target molecule can undergo oxidation by this reactive oxygen species and the reaction needs dissolved O₂ to proceed, therefore the reaction is classified as ¹O₂‐mediated oxidation (type II mechanism). However, this assumption is not always correct, and as an example, a study on the degradation of 2′‐deoxyguanosine 5′‐monophosphate photosensitized by pterin is presented. A general mechanism is proposed to explain how the degradation of biological targets, such as nucleotides, photosensitized by pterins, naturally occurring ¹O₂ photosensitizers, takes place through an electron‐transfer‐initiated process (type I mechanism), whereas the contribution of the ¹O₂‐mediated oxidation is almost negligible.     

Determination of marker pteridins and biopterin reduced forms, tetrahydrobiopterin and dihydrobiopterin, in human urine, using a post-column photoinduced fluorescence liquid chromatographic derivatization method

A liquid chromatographic method for the simultaneous analysis of marker pteridins and biopterin reduced forms, in urine samples is proposed. A Zorbax Eclipse XDB-C18 column was used for the chromatographic separation, using a 98/2 (v/v), citrate buffer (pH 5.5)-acetonitrile mobile phase, in isocratic mode. A post-column photoderivatization was carried out with an on-line photoreactor, located between a diode array detector (DAD) and a fast scanning fluorescence detector (FSFD). Neopterin (NEO), biopterin (BIO), pterin (PT) and dihydrobiopterin (BH2) were determined by measuring native fluorescence, using the photoreactor in OFF-mode, and tetrahydrobiopterin (BH4) was determined by measuring of the induced fluorescence of the generated photoproducts, using the photoreactor in ON-mode. In addition, Creatinine (CREA), as a reference of metabolites excrection in urine, was simultaneously determined using the DAD detector. Detection limits were 0.2, 13.0, 0.3, 0.3 and 3.5 ng mL⁻¹, for NEO, BH2, BIO, PT and BH4, respectively, and 0.4 μg mL⁻¹ for CREA. Ratio values for NEO/CREA, PT/CREA, BH4/CREA, BH2/CREA, NEO/BIO and BIO_total/CREA, in urine samples, of healthy children and adults, phenylketonuric children and infected mononucleosis children, are reported. A comparative study, about the mean values obtained for each of the compounds, by the present procedure and by the classical iodine oxidation method (Fukushimás method), has been performed, in urine samples belonging to healthy volunteers. The values obtained were BH4/CREA: 0.41, BH2/CREA: 0.31 and BIO_total/CREA: 0.73, by the proposed method, and BH4/CREA: 0.35, BH2/CREA: 0.20 and BIO_total/CREA: 0.48, by iodine oxidation method.     

Synthesis of 7-methyl-6-indolopterin and 7-methyl-6-indoloquinoxaline

The first syntheses of indolopterin and indoloquinoxaline, two important and dissimilar diheterocycles linking C-2 of indole with C-6 of pterin (significant positions for showing biological activity), and quinoxaline, respectively, have been achieved based on two classical reactions. The introduction of a keto methyl group on to the 6-position of pterin and quinoxaline followed by Fischer indole synthesis led to these target diheterocycles. These indole-substituted diheterocycles will significantly increase the electron density on the pterin-5-N and quinoxazoline-2-N, which may change the redox properties of pterin and quinoxaline, and also the electron-withdrawing pterin or quinoxazoline should make the indole NH more acidic.     

Functional model of oxomolybdoenzymes: Synthesis and characterization of a molybdenum complex with sulphur and pterin ligands exhibiting saturation kinetics with pyridine N-oxide

Redox reaction between 6-acetonylisoxanthopterin (H₂pte) and [Mo^VIO₂ (ssp)] [ssp = anion of 2-(salicylideneamino) benzenethiol] in CH₃OH-C₂H₅OH medium produces a new mixed ligand compound [Mo^IV (ssp) (Hpte) (OCH₃)] (1). It has been characterized by elemental analysis, ESMS data, UV-Vis, IR,¹HNMR (1D and 2D) spectroscopy and cyclic voltammetry. Kinetics of formation of this compound as well as that of its reaction with pyridine N-oxide have been followed spectrophotometrically. Both the reactions follow substrate saturation kinetics and involve metal-centred oxygen atom transfer process. Large negative values of entropy of activation indicate the operation of associative mechanism.     

Synthesis,Redox and Spectroscopic Properties of Pterin of Molybdenum Cofactors

Pterins are bicyclic heterocycles that are found widely across Nature and are involved in a variety of biological functions. Notably, pterins are found at the core of molybdenum cofactor (Moco) containing enzymes in the molybdopterin (MPT) ligand that coordinates molybdenum and facilitates cofactor activity. Pterins are diverse and can be widely functionalized to tune their properties. Herein, the general methods of synthesis, redox and spectroscopic properties of pterin are discussed to provide more insight into pterin chemistry and their importance to biological systems.     

Pterin-based highly selective,ratiometric, and sensitive ‘naked-eye’ sensor for acetate

The design and synthesis of a new pterin-based ratiometric and sensitive ‘naked-eye’ sensor R for highly selective recognition of acetate are reported. The acidic lactam NH and the NH of 2-N-pivaloyl group of receptor R along with 2,4-dinitrophenyl hydrazone group having the other acidic NH moiety lead to the binding of acetate anion in a 1:2 ratio by change of spectroscopic behavior on complexation (UV–vis and ¹H NMR studies) which is also proven by Job plot. The sharp color change from light yellow to violet promises R to be a useful chromogenic ratiometric sensor for acetate amongst other common anions.     

SNH reactions of 1,2,4-triazine N-oxides,pyrazine N-oxides,and pterin N-oxides with arenethiols*

1,2,4-Triazine 4-oxides were found to enter into the reactions of nucleophilic substitution of hydrogen with S-nucleophiles (arenethiols) in the presence of acylating agents and trifluoroacetic acid. The reactions proceeded with loss of the N-oxide function to form 5-arylthio-1,2,4-triazines. 2-Amino-3-ethoxycarbonylpyrazine 1-oxides and 2-amino-4-oxopterin 8-oxides react with arenethiol analogously.     

Identification and energetic ranking of possible docking sites for pterin on dihydrofolate reductase

The reliability of new methodology for detecting sites for ligand binding on the surfaces of proteins has been tested using a range of dihydrofolate reductase (DHFR) crystal structures. Docking of the pterin molecule to ten such DHFR structures has been examined. Initial docking sites were selected using the VDW-FFT method we have developed recently. This procedure was followed by rigid geometry optimization and solvation energy calculations using our parametrized reaction field multipoles (PRFM) method and the finite difference solution of the Poisson equation (FDPB) method. Two different sets of MM parameters, from the OPLS and Amber94 force fields, have been used. In eight cases the energy of the complexes with pterin bound at the active site was the lowest with the recent Amber94 parameters. In one case the spurious first-ranked site was only 1.8 kcal/mol lower in energy compared with the active site. The other failure of the method may, in fact, represent a valid initial binding site. The calculations with the old OPLS parameters gave slightly worse results.     

高效液相色谱法同时测定尿中新喋呤和生物喋呤

建立了同时分离检测尿中新喋呤（neopterin,NP）和生物喋呤(biopterin,BP)的高效液相色谱（HPLC）-荧光检测方法。采用Hypersil BDS C18柱、甲醇-水(体积比为10∶90)流动相(流速0.5 mL/min)、激发波长360 nm、发射波长 440 nm、柱温20 ℃的色谱条件,同时分离测定了尿中的NP和BP。尿标本经三氯乙酸处理,在4 ℃下,以12000 r/min的速率离心15 min,上清液用碱中和后,取30　μL直接进样。研究结果表明,NP的线性范围为0.12～10