Intramolecular nitrone cycloaddition reaction on carbohydrate-based precursors: application in the synthesis of spironucleosides and spirobisnucleosides

A simple synthesis of chiral spironucleosides and spirobisnucleosides is described. Intramolecular 1,3-dipolar nitrone cycloaddition reaction of d-glucose-derived precursors having olefin at C-3 and nitrone at C-5, C-1, or C-2 (in nor-series) furnished bisisoxazolidinospirocycles 4-7, 11, and 12 in good yields. Reductive ring opening of the isoxazolidine moieties in 4-6 followed by construction of a nucleoside base upon the generated amino groups smoothly yielded spirobisnucleosides 17 and 18 and spironucleosides 20 and 21.     

A Leslie-Gower Holling-type II ecoepidemic model

The modified Leslie-Gower and Holling-type II predator-prey model is generalized in the context of ecoepidemiology, with disease spreading only among the prey species. A new feature is introduced, the intraspecific competition of infected prey. All the equilibria are characterized and the existence of a Hopf bifurcation at the coexistence equilibrium is shown.     

Fabrication of carbohydrate microarrays through boronate formation

A straightforward method for fabricating a stable and covalent carbohydrate microarray based on boronate formation between the hydroxyl groups of carbohydrate and boronic acid (BA) on the glass surface was used to identify carbohydrate-protein interactions.     

Analysis of Bogdanov–Takens bifurcations in a spatiotemporal harvested-predator and prey system with Beddington–DeAngelis-type response function

Nonlinear Dynamics - In this article, we consider a predator–prey system with constant rate of harvesting, which exhibits Hopf and Bogdanov–Takens bifurcations under certain parametric...     

Ratio-dependent predator–prey model of interacting population with delay effect

A system of delay differential equation is proposed to account the effect of delay in the predator?Cprey model of interacting population. In this article, the modified ratio-dependent Bazykin model with delay in predator equation has been considered. The essential mathematical features of the proposed model are analyzed with the help of equilibria, local and global stability analysis, and bifurcation theory. The parametric space under which the system enters into a Hopf-bifurcation has been investigated. Global stability results are obtained by constructing suitable Lyapunov functions. We derive the explicit formulae for determining the stability, direction, and other properties of bifurcating periodic solutions by using normal form and central manifold theory. Using the global Hopf-bifurcation result of Wu (Trans. Am. Math. Soc., 350:4799?C4838, 1998) for functional differential equations, the global existence of periodic solutions has been established. Our analytical findings are supported by numerical experiments. Biological implication of the analytical findings are discussed in the conclusion section.     

Synthesis of N-modified sTn analogs and evaluation of their immunogenicities by microarray-based immunoassay

A series of sTn derivative-keyhole limpet hemocyanin (KLH) conjugates were synthesized, and their immunogenicities were evaluated by corresponding IgG production. To achieve a high-throughput screening immunoassay, a glycan microarray with sTn and its analogs was used to detect the production of corresponding antibodies in mouse sera. The immunoassay results revealed that the derived sTn antigens are generally more immunogenic than the parent sTn antigen. The N-propionyl sTn antigen was the most immunogenic among the sTn derivatives investigated, and its antiserum was cross-reactive with natural sTn. These results indicate that N-propionyl sTn may serve as a viable vaccine candidate to produce antibody for detection of sTn antigen.     

Nucleoside synthesis from 3-alkylated sugars: role of 3beta-oxy substituents in directing nucleoside formation

Using Vorbrüggen's protocol, reaction of persilylated uracil with xylofuranose derivatives having 3beta-oxy-3alpha-alkyl substitution produced both alpha- and beta-nucleosides. Only the beta-nucleosides were formed from substrates having the reverse stereochemistry at C-3 or lacking the 3-alkyl substituent. Participation of the 3beta-oxy substituent in stabilizing the incipient C-1 carbonium ion (or oxonium ion) intermediate has been suggested from analysis of energy-minimized conformations.     

Sequential ring-closing metathesis and nitrone cycloaddition on glucose-derived substrates: a divergent approach to analogues of spiroannulated carbanucleosides and conformationally locked nucleosides

The carbohydrate-derived substrate 3-C-allyl-1,2:5,6-di-O-isopropylidene-alpha-D-allofuranose was judiciously manipulated for preparing suitable synthons, which could be converted to a variety of isoxazolidino-spirocycles and -tricycles through the application of ring-closing metathesis (RCM) and intramolecular nitrone cycloaddition (INC) reactions. Cleavage of the isoxazolidine rings of some of these derivatives by transfer hydrogenolysis followed by coupling of the generated amino functionalities with 5-amino-4,6-dichloropyrimidine furnished the corresponding chloropyrimidine nucleosides, which were elaborated to spiroannulated carbanucleosides and conformationally locked bicyclo[2.2.1]heptane/oxa-bicyclo[3.2.1]octane nucleosides. However, use of higher temperature for the cyclization of one of the chloropyrimidines led to the dimethylaminopurine analogue as a sole product, formed via nucleophilic displacement of the chloro group by dimethylamine generated from DMF.