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21.
Georgii V. Bobkov Sergey N. Mikhailov Arthur Van Aerschot Piet Herdewijn 《Tetrahedron》2008,64(27):6238-6251
A simple and efficient method for the preparation of eight phosphoramidite building blocks for incorporation of 2′-O-(2-aminoethoxymethyl)ribonucleosides and 2′-O-(3-aminopropoxymethyl)ribonucleosides into synthetic oligonucleotides has been developed. The synthetic routes are maximally convergent and provide sufficient amounts of phosphoramidites for several solid-phase synthesis coupling reactions. Using acyclic derivatives 17a,b the overall yields of phosphoramidites 2 and 3 were increased up to 50% for pyrimidine nucleosides and up to 30% for purine derivatives with substantial decrease of total reaction steps. The 2′-O-substituent was found to be stable during oligonucleotide synthesis. The resulting oligonucleotides are of particular interest for post-synthetic functionalization and conjugation. 相似文献
22.
Dr. Shrinivas Dumbre Dr. Valérie Pezo Guy Schepers Prof. Vitor B. Pinheiro Prof. Eveline Lescrinier Prof. Philipp Holliger Dr. Philippe Marlière Prof. Piet Herdewijn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(13):5009-5022
The synthesis, base‐pairing properties and in vitro and in vivo characteristics of 5‐methyl‐isocytosine (isoCMe) and isoguanine (isoG) nucleosides, incorporated in an HNA(h) (hexitol nucleic acid)–DNA(d) mosaic backbone, are described. The required h‐isoG phosphoramidite was prepared by a selective deamination as a key step. As demonstrated by Tm measurements the hexitol sugar showed slightly better mismatch discrimination against dT. The d‐isoG base mispairing follows the order T>G>C while the h‐isoG base mispairing follows the order G>C>T. The h‐ and d‐isoCMe bases mainly mispair with G. Enzymatic incorporation experiments show that the hexitol backbone has a variable effect on selectivity. In the enzymatic assays, isoG misincorporates mainly with T, and isoCMe misincorporates mainly with A. Further analysis in vivo confirmed the patterns of base‐pair interpretation for the deoxyribose and hexitol isoCMe/isoG bases in a cellular context, through incorporation of the bases into plasmidic DNA. Results in vivo demonstrated that mispairing and misincorporation was dependent on the backbone scaffold of the base, which indicates rational advances towards orthogonality. 相似文献
23.
Wu T Froeyen M Kempeneers V Pannecouque C Wang J Busson R De Clercq E Herdewijn P 《Journal of the American Chemical Society》2005,127(14):5056-5065
24.
Misuraca MC Grecu T Freixa Z Garavini V Hunter CA van Leeuwen PW Segarra-Maset MD Turega SM 《The Journal of organic chemistry》2011,76(8):2723-2732
A family of four biscarbamates (AA) and four bisphenols (DD) were synthesized, and H-bonding interactions between all AA?DD combinations were characterized using (1)H NMR titrations in carbon tetrachloride. A chemical double mutant cycle analysis shows that there are no secondary electrostatic interactions or allosteric cooperativity in these systems, and the system therefore provides an ideal platform for investigating the relationship between chemical structure and chelate cooperativity. Effective molarities (EMs) were measured for 12 different systems, where the number of rotors in the chains connecting the two H-bond sites was varied from 5 to 20. The association constants vary by less than an order of magnitude for all 12 complexes, and the variation in EM is remarkably small (0.1-0.9 M). The results provide a relationship between EM and the number of rotors in the connecting chains (r): EM ≈ 10r(-3/2). The value of 10 M is the upper limit for the value of EM for a noncovalent intramolecular interaction. Introduction of rotors reduces the value of EM from this maximum in accord with a random walk analysis of the encounter probability of the chain ends (r(-3/2)). Noncovalent EMs never reach the very high values observed for covalent processes, which places limitations on the magnitudes of the effects that one is likely to achieve through the use of chelate cooperativity in supramolecular assembly and catalysis. On the other hand, the decrease in EM due to the introduction of conformational flexibility is less dramatic than one might expect based on the behavior of covalent systems, which limits the losses in binding affinity caused by poor preorganization of the interaction sites. 相似文献
25.
Stanković S Catak S D'hooghe M Goossens H Abbaspour Tehrani K Bogaert P Waroquier M Van Speybroeck V De Kimpe N 《The Journal of organic chemistry》2011,76(7):2157-2167
The synthetic utility of N-alkylidene-(2,3-dibromo-2-methylpropyl)amines and N-(2,3-dibromo-2-methylpropylidene)benzylamines was demonstrated by the unexpected synthesis of 3-methoxy-3-methylazetidines upon treatment with sodium borohydride in methanol under reflux through a rare aziridine to azetidine rearrangement. These findings stand in contrast to the known reactivity of the closely related N-alkylidene-(2,3-dibromopropyl)amines, which are easily converted into 2-(bromomethyl)aziridines under the same reaction conditions. A thorough insight into the reaction mechanism was provided by both experimental study and theoretical rationalization. 相似文献
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The study of theacidic sites in zeolites is important to understand the nature of the acidic catalyticfunction.…… 《催化学报》2001,22(3):219-220
The study of the acidic sites in zeolites is important to understand the nature of the acidic catalytic function. 相似文献
30.
Based on our analysis of the hopcount of the shortest path between two arbitrary nodes in the class G
p
(N) of random graphs, the corresponding flooding time is investigated. The flooding time T
N
(p) is the minimum time needed to reach all other nodes from one node. We show that, after scaling, the flooding time T
N
(p) converges in distribution to the two-fold convolution (2*) of the Gumbel distribution function (z)=exp (–e
–z
), when the link density p
N
satisfies Np
N
/(log N)3 if N . 相似文献