Synthesis and reaction of 6-trialkylsilyl substituted uracils and uridines

6-Trimethylsilyl substituted 1,3-dimethyluracil and uridine were prepared via lithiation and successive trapping with trimethylsilylchloride in the presence of 4-dimethylaminopyridine and converted to 5,6-dihalogenated derivatives by treatment with NBS or NCS.     

Ab initio molecular orbital study on the G-selectivity of GGG triplet in copper(I)-mediated one-electron oxidation

The G-selectivity for Cu(I)-mediated one-electron oxidation of 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3' has been examined by ab initio molecular orbital calculations. It was confirmed that G(1) is selectively damaged by Cu(I) ion for both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', being good agreement with experimental results. The Cu(I)-mediated G(1)-selectivity is primarily due to the stability of the Cu(I)-coordinated complex, [-XG(1)G(2)G(3)-,-Cu(I)(H(2)O)(3)](+). The Cu(I) ion coordinates selectively to N7 of G(2) of 5'-G(1)G(2)G(3)-3' rather than N7 of G(1). The G(2)-selective coordination induces the G(1)-selective trap of a hole that is created by one-electron oxidation and migrates to GGG triplet. Therefore, the radical cation of G(1) is selectively created in both 5'-TG(1)G(2)G(3)-3' and 5'-CG(1)G(2)G(3)-3', giving the G(1)-selective damage of 5'-G(1)G(2)G(3)-3'.     

Glycopolymeric inhibitors of β-glucuronidase. II. Synthesis of glycopolymers containing pendant L-gulonic moieties and effects of the carboxyl group in the glycopolymers upon the activity of β-glucuronidase

A new styrene derivative having an L -gulonic moiety, N-(p-vinylbenzyl)-6-L -gulonamide (VB-6-Glco, 3) was synthesized from L -gulono-1,4-lactone and p-vinylbenzylamine. The styrene derivative (3) was subjected to the radical homopolymerization and copolymerization with acrylamide and acrylic acid. The hydrolysis of p-nitrophenyl β-D -glucuronide with β-glucuronidase was scarcely inhibited in the presence of the glycopolymer prepared from 3 and acrylamide (P(VB-6-Glco-co-AAm), 4), whereas the glycopolymer prepared from 3 and acrylic acid (P(VB-6-Glco-co-AAK), 5) was found to suppress the enzyme activity strongly as well as a polystyrene derivative having pendant D -glucaric moieties (P(VB-6-GlcaH-co-AAm), 6). From the kinetic analysis of the hydrolysis, the glycopolymers 6 and 5 were postulated to inhibit the enzyme competitively and uncompetitively, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2773–2779, 1999     

Elastic modulus of the crystalline regions of polyimide derived from poly(amic acid)–biphtalic dianhydride and p-phenylene diamine

The elastic modulus E_l of the crystalline regions in the direction parallel to the chain axis was measured by X-ray diffraction for polyimide derived from polyamic acid (biphthalic dianhydride and p-phenylene diamine). These specimens were cured by two different routes: curing at 200 °C, and at 400 °C for 1 h, respectively (2STEPS), and curing from 80 °C to 400 °C stepwise (nine steps) for 1 h at each step (STEPWISE). The E_l values of 54–169 GPa were obtained for the STEPWISE specimen and 80–178 GPa for the 2STEPS specimen, depending on the meridional reflection employed for measurement of the E_l value. A linear relationship between the E_l value and the fiber identity period was obtained from each meridional diffraction, such that the E_l value increased with an increase in the fiber identity period. The E_l value of the fully extended structure was estimated to be 210 GPa. These are considered to be due to the coexistence of polymorphs with different skeletal structures. The crystalline regions of the 2STEPS specimen seems to consist of a more extended skeleton than those of the STEPWISE specimen. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3294–3301, 1999     

Closure, 2-factors,and cycle coverings in claw-free graphs

In this article, we study cycle coverings and 2-factors of a claw-free graph and those of its closure, which has been defined by the first author (On a closure concept in claw-free graphs, J Combin Theory Ser B 70 (1997), 217–224). For a claw-free graph G and its closure cl(G), we prove: (1) V(G) is covered by k cycles in G if and only if V(cl(G)) is covered by k cycles of cl(G); and (2) G has a 2-factor with at most k components if and only if cl(G) has a 2-factor with at most k components. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 109–117, 1999     

Laser-irradiation-induced surface graft polymerization method

A laser-induced surface graft polymerization method is reported in which surface radicals generated upon laser irradiation initiated radical polymerization. The radical concentrations generated upon excimer laser irradiation under vacuum on poly-(ethylene terephthalate) film surfaces were measured using a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl. The density of surface radicals increased with laser fluence at low fluences but decreased at high fluences. Upon laser irradiation and subsequent treatment with gaseous N,N-dimethylacrylamide, surface graft polymerization occurred. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 747–750, 1997     

Sequence‐Specific DNA Alkylation by Hybrid Molecules between Segment A of Duocarmycin A and Pyrrole/Imidazole Diamide

In the absence of distamycin A (Dist), hybrids 1 (X=N, CH) selectively alkylate the 3′ end of adenine in AT‐rich DNA sequences. However, these hybrids can form a heterodimer with Dist to alkylate G residues of predetermined DNA sequences efficiently and with high selectivity.     

Ring-opening fluorination of bicyclic azaarenes

We have discovered a ring-opening fluorination of bicyclic azaarenes. Upon treatment of bicyclic azaarenes such as pyrazolo[1,5-a]pyridines with electrophilic fluorinating agents, fluorination of the aromatic ring is followed by a ring-opening reaction. Although this overall transformation can be classified as an electrophilic fluorination of an aromatic ring, it is a novel type of fluorination that results in construction of tertiary carbon–fluorine bonds. The present protocol can be applied to a range of bicyclic azaarenes, tolerating azines and a variety of functional groups. Additionally, mechanistic studies and enantioselective fluorination have been examined.

A ring-opening fluorination of bicyclic azaarenes was developed. Although this overall transformation can be classified as an electrophilic fluorination of aromatics, it is a novel type of fluorination that results in construction of tert-C–F bonds.