Littérature scientifique sur le sujet « Diaminopurine »

Treatment of 2,6-diaminopurine riboside (2-aminoadenosine) with α-acetoxyisobutyryl bromide in acetonitrile gave mixtures of the trans 2′,3′-bromohydrin acetates 2. Treatment of 2 with zinc–copper couple effected reductive elimination, and deprotection gave 2,6-diamino-9-(2,3-dideoxy-β-D-erythro-pent-2-enofuranosyl)purine (3a). Treatment of 2 with Dowex 1 × 2 (OH−) resin in methanol gave the 2′,3′-anhydro derivative 4. Stannyl radical-mediated hydrogenolysis of 2 and deprotection gave the 2′-deoxy 6a and 3′-deoxy 7a nucleosides. Treatment of the 3′,5′-O-(tetraisopropyldisiloxanyl) derivative (5a) with trifluoromethanesulfonyl chloride – 4-(dimethylamino)pyridine gave 2′-triflate 5c. Displacement with lithium azide–dimethylformamide and deprotection gave the arabino 2′-azido derivative 8a, which was reduced to give 2,6-diamino-9-(2-amino-2-deoxy-β-D-arabinofuranosyl)purine (8b). Sugar-modified 2,6-diaminopurine nucleosides were treated with adenosine deaminase to give the corresponding guanine analogues. Keywords: adenosine deaminase, 2,6-diaminopurine nucleosides, deoxygenation, guanine nucleosides, nucleosides.

Base-catalyzed reactions of diethyl [(oxiranylmethoxy)methyl]phosphonate (2) with purine bases (adenine, 2,6-diaminopurine, 6-chloropurine and 2-amino-6-chloropurine) gave corresponding 9- or 7-[2-hydroxy-3-(phosphonomethoxy)propyl] purines. The adenine and 2,6-diaminopurine derivatives cyclize to cyclic phosphonates 4 and 6. The 9-[2-hydroxy-3-(phosphonomethoxy)propyl] derivatives of N6-substituted adenine and 2,6-diaminopurine (15-27) were prepared by the treatment of diethyl {[3-(6-chloropurin-9-yl)-2-hydroxypropoxy]methyl}phosphonate (11) or diethyl {[3-(2-amino-6-chloropurin-9-yl)-2-hydroxypropoxy]methyl}phosphonate (13) with primary or secondary amines. The reaction of 6-chloro- or 2-amino-6-chloropurine derivatives (11, 13) with thiourea gave the corresponding diethyl purine-6-thiol or 2-aminopurine-6-thiol phosphonates 47, 48. The guanine derivative 49 was prepared by the treatment of compound 13 with 80% acetic acid. All diethyl phosphonates were transformed to free phosphonic acids (31-43, 50-52) by the action of bromotrimethylsilane and subsequent hydrolysis.

The electronic relaxation pathways of 2,6-diaminopurine and its deoxyribonucleoside were elucidated in aqueous solution. It is shown that these purine derivatives are largely photostable to ultraviolet radiation.

Abstract Single molecule experiments have demonstrated a progressive transition from a B- to an L-form helix as DNA is gently stretched and progressively unwound. The particular sequence of a DNA segment defines both base stacking and hydrogen bonding that affect the partitioning and conformations of the two phases. Naturally or artificially modified bases alter H-bonds and base stacking and DNA with diaminopurine (DAP) replacing adenine was synthesized to produce linear fragments with triply hydrogen-bonded DAP:T base pairs. Both unmodified and DAP-substituted DNA transitioned from a B- to an L-helix under physiological conditions of mild tension and unwinding. This transition avoids writhing and the ease of this transition may prevent cumbersome topological rearrangements in genomic DNA that would require topoisomerase activity to resolve. L-DNA displayed about tenfold lower persistence length than B-DNA. However, left-handed DAP-substituted DNA was twice as stiff as unmodified L-DNA. Unmodified DNA and DAP-substituted DNA have very distinct mechanical characteristics at physiological levels of negative supercoiling and tension.

In the last few decades, the constant development of novel microscopy techniques have created the basis for a new paradigm in the field of biophysics. Single-molecule techniques enabled to carry out experiments providing new information: the nanomanipulation of individual biomolecules revealed unknown insights into the elasticity and mechanics of molecules, improving the understanding of the fundamental relation between structural properties and biological functions. In particular, an AFM and mostly a MT setup were used during this thesis work, both located in biophysics laboratory of Prof. Francesco Mantegazza, at the University of Milano-Bicocca. Similar issues were encountered at the cellular level, because bulk experiments of conventional microscopy techniques provide information on average only, without taking into account the intrinsic biological heterogeneity. Recent developments in microfluidics enabled to follow individual cells over a long time and under controlled conditions. During the last part of this thesis project I used one of these microfluidic devices to perform time-lapse microscopy experiments at the single-cell level. These experiments were carried out during a visiting period of seven months in Prof. Pietro Cicuta’s laboratory, in Cavendish laboratory at University of Cambridge. In this thesis I dealt with three main research topics: • DNA structural polymorphism • nanomechanics of DNA-ligand interactions • the dual role of H-NS protein: DNA condensation and gene regulation The study of the conformational changes of DNA, namely the property of structural polymorphism, is addressed during two projects: one about the nanomechanics of a DNA analogue and another concerning the behavior of DNA at high supercoiling. The study of a DNA analogue enables to observe how a chemical modification of nucleotides can induce structural re- arrangements of the double-helix, biasing towards an A-like-form of DNA. The regimes of high supercoiling, both positive and negative supercoiling, show instead how an applied torsion at a certain forces can promote the formation of plectonemes or denaturation bubbles, which are conditions that favor particular structural transitions. The second major theme concerns the analysis of the nanomechanics of DNA-ligand complexes, particularly the interactions of DNA with anticancer drugs or with the H-NS protein and the crowding agent PEG. The project about the interactions between DNA and drugs clearly shows how the mechanical properties and the stability of DNA change due to the binding with compounds commonly used in clinics to treat tumors. On the other hand, the H-NS protein forms relatively stable DNA loops and influences the stability of the double helix, as well as the crowding agent. The protein binding mechanism has a preference for some DNA sequences and an unexpected concentration-dependent behavior. The analysis of the the DNA-H-NS interactions also enables, particularly in crowding conditions, to better understand the mechanism of DNA condensation inside the cell, one of the biological roles of H-NS. The second important function of this NAP is the gene regulation. To investigate the dual role of H-NS in great detail two complementary techniques have been combined. The nanoma- nipulation technique is employed to observe the structural role of H-NS and its combined activity with a crowding agent leading to a clear and abrupt compaction of DNA. Time-lapse fluorescence microscopy is instead used to study the regulatory role of the protein, more precisely the gene silencing mechanism, at the single-cell level. This activity has also a strong influence in the cell physiology, by significantly changing the growth rate of bacteria.
In the last few decades, the constant development of novel microscopy techniques have created the basis for a new paradigm in the field of biophysics. Single-molecule techniques enabled to carry out experiments providing new information: the nanomanipulation of individual biomolecules revealed unknown insights into the elasticity and mechanics of molecules, improving the understanding of the fundamental relation between structural properties and biological functions. In particular, an AFM and mostly a MT setup were used during this thesis work, both located in biophysics laboratory of Prof. Francesco Mantegazza, at the University of Milano-Bicocca. Similar issues were encountered at the cellular level, because bulk experiments of conventional microscopy techniques provide information on average only, without taking into account the intrinsic biological heterogeneity. Recent developments in microfluidics enabled to follow individual cells over a long time and under controlled conditions. During the last part of this thesis project I used one of these microfluidic devices to perform time-lapse microscopy experiments at the single-cell level. These experiments were carried out during a visiting period of seven months in Prof. Pietro Cicuta’s laboratory, in Cavendish laboratory at University of Cambridge. In this thesis I dealt with three main research topics: • DNA structural polymorphism • nanomechanics of DNA-ligand interactions • the dual role of H-NS protein: DNA condensation and gene regulation The study of the conformational changes of DNA, namely the property of structural polymorphism, is addressed during two projects: one about the nanomechanics of a DNA analogue and another concerning the behavior of DNA at high supercoiling. The study of a DNA analogue enables to observe how a chemical modification of nucleotides can induce structural re- arrangements of the double-helix, biasing towards an A-like-form of DNA. The regimes of high supercoiling, both positive and negative supercoiling, show instead how an applied torsion at a certain forces can promote the formation of plectonemes or denaturation bubbles, which are conditions that favor particular structural transitions. The second major theme concerns the analysis of the nanomechanics of DNA-ligand complexes, particularly the interactions of DNA with anticancer drugs or with the H-NS protein and the crowding agent PEG. The project about the interactions between DNA and drugs clearly shows how the mechanical properties and the stability of DNA change due to the binding with compounds commonly used in clinics to treat tumors. On the other hand, the H-NS protein forms relatively stable DNA loops and influences the stability of the double helix, as well as the crowding agent. The protein binding mechanism has a preference for some DNA sequences and an unexpected concentration-dependent behavior. The analysis of the the DNA-H-NS interactions also enables, particularly in crowding conditions, to better understand the mechanism of DNA condensation inside the cell, one of the biological roles of H-NS. The second important function of this NAP is the gene regulation. To investigate the dual role of H-NS in great detail two complementary techniques have been combined. The nanoma- nipulation technique is employed to observe the structural role of H-NS and its combined activity with a crowding agent leading to a clear and abrupt compaction of DNA. Time-lapse fluorescence microscopy is instead used to study the regulatory role of the protein, more precisely the gene silencing mechanism, at the single-cell level. This activity has also a strong influence in the cell physiology, by significantly changing the growth rate of bacteria.

Thesis (M.S.)--University of Wisconsin--Madison, 2002.
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Acyclic nucleoside phosphonates (ANP) are broad-spectrum antivirals highly effective against herpes-, retro- and hepadnaviruses. They also exhibit cytostatic, antiparasitic, immunomodulatory activities. Their transdermal delivery offers an attractive and advantageous route of administration, but is limited due to the polar character of their phosphonate moiety. The aim of this work was to study the possibility of both transdermal and dermal application of a series of 2,6-diaminopurine derivatives including (R)-PMPDAP and (S)-PMPDAP, (S)-HPMPDAP, (S)-8-azaHPMPDAP, cyclic (S)-HPMPDAP and lysolipid prodrugs, i.e., hexadecyloxypropyl (HDP) esters of (R)-HDP-PMPDAP and (S)-HDP- HPMPDAP. Ability of ANP to penetrate trough the skin by themselves is generally very low. For this reason the influence of permeation enhancer dodecylester of 6- (dimethylamino)hexanoic acid (DDAK) through and into human skin was investigated. The evaluation was performed in vitro by using Franz diffusion cells and human skin. The results of this work confirm that ANP (60 mM in 60 % propylene glycol) delivery through the skin is very low (flux 0.53-1.40 nmol/cm2 /h), except for the lysolipid prodrugs (R)-HDP-PMPDAP and (S)-HDP-HPMPDAP), which were not detected in the acceptor phase at all. 1 % DDAK enhanced transdermal flux of...