Synthesis of the Methyl α-Glycoside of the Intracatenary Disaccharide Repeating Unit of the O-Polysaccharide of Vibrio Cholerae O:1. A Comparison of two Assembly Strategies

Abstract

The two strategies engaged in the construction of the title disaccharide 17 comprise: 1. assembly of a diamino disaccharide and its N-acylation using chiral reagents to introduce the 4-(3-deoxy-l-glycero-tetronyl) group, followed by deprotection, and 2. preparation of a glycosyl acceptor and a glycosyl donor both having the chiral 3-deoxy-l-glycero-tetronamido group already in place, their condensation to give a fully substituted disaccharide, and deprotection. Accordingly, the crystalline diamino disaccharide methyl 2-O-(4-amino-3-O-benzyl-4, 6-dideoxy-α-d-mannopyranosyl)-4-amino-3-O-benzyl-4, 6-dideoxy-α-d-mannopyranoside, (14), was prepared from the known [Bundle, D. R. et al., Carbohydr. Res. 174, 239 (1988)] diazido disaccharide 12, and treated with the lactone 30, or its acetylated or benzylated analogs 31 and 32, respectively, as the N-acylating reagents. Subsequent deprotection of the respective products applying standard chemistry gave 17. Alternatively, the methyl α-glycoside of the monomeric intracatenary repeating unit of Vibrio cholerae 0:1 (2) was converted to the fully benzoylated glycosyl chloride 26, and the latter glycosyl donor was condensed with methyl 3-O-benzyl-4,6-dideoxy-4-(2,4-di-O-benzoyl-3-deoxy- l-glycero-tetronamido)-α-d-mannopyranoside (24), to give the corresponding, fully protected derivative 27. Deprotection then readily gave 17. It appears that the title disaccharide can be most efficiently synthesized using synthons 24 and 26. The lactones 30 and 32 appear to be promising acylating reagents for the introduction of the 3-deoxy-l-glycero-tetronamido group when higher oligosaccharides in this series will be synthesized via their (poly)amino precursors.     

The Reaction of Methyl 3-O-Benzyl-4, 6-O-benzylidene-α-D-mannopyranqside with Diethylaminosulfur Trifluoride (DAST)

Methyl 3-O-benzyl-4, 6-O-benzylidene-α-D-mannopyranoside (2), when treated in diglyme at 1000[ddot] with DAST, undergoes a rapid reaction involving the participation of the axial methoxyl group at C-1 to give 3-O-benzyl-4, 6-O-benzylidene-2-O-methyl-α- (4) and β-D-gluco-pyranosyl fluoride (3), isolated in a combined yield of 75-80%. In the presence of pyricfine and at room temperature, the major product formed is methyl 3-O-benzyl-4, 6-O-benzylidene-2-deoxy-α-D-eiythro-hex-2-enopyranoside (11). The structures 3, 4 and 11 have been confirmed by analysis of their NMR spectral data, as well as by chemical transformations into compounds of established structure.     

The first example of a crystallization-induced asymmetric transformation (CIAT) in the Mannich reaction

The novel synthesis of highly enantioenriched N-substituted α-amino-γ-alkyl(aryl)-γ-oxobutanoic acids is described. The process involves the combination of a crystallization-induced asymmetric transformation (CIAT) and the Mannich reaction. The role of retro-Mannich and retro-Michael reactions in the mechanism of the highly stereoselective transformation is also discussed.     

Ab initio theory of complex electronic ground state of superconductors: II.: Antiadiabatic state—Ground state of superconductors

Based on Q, P-dependent modification of the Born-Oppenheimer approximation (BOA), the ab initio theory of complex electronic ground state of superconductors is presented. As an illustrative example, application of the theory to superconductors of a different character and to the corresponding nonsuperconducting analogues is presented. It is shown that due to electron-phonon (EP) interactions, which drive system from adiabatic into antiadiabatic state, adiabatic translation symmetry is broken and system is stabilized in antiadiabatic state at distorted geometry with respect to adiabatic equilibrium high-symmetry structure. Stabilization effect in the antiadiabatic state is due to strong dependence of the electronic motion on the instantaneous nuclear kinetic energy, i.e. on the effect that is neglected on the adiabatic level within the BOA. At distorted geometry, antiadiabatic ground state is geometrically degenerated with fluxional nuclear configurations in the phonon modes that drive system into this state. It has been shown that until the system remains in antiadiabatic state, nonadiabatic polaron-renormalized phonon interactions are zero in the well-defined k-region of reciprocal lattice. This, along with geometric degeneracy of the antiadiabatic state, enables formation of mobile bipolarons that can move over lattice as supercarriers without dissipation. Moreover, it has been shown that due to EP interactions at transition into antiadiabatic state, k-dependent gap in one-electron spectrum has been opened. Gap opening is associated with shift of the original adiabatic Hartree-Fock orbital energies and with the k-dependent change in density of states of particular band(s) at Fermi level. Corrected one-particle spectrum enables to derive thermodynamic properties in full agreement with corresponding thermodynamic properties of superconductors.Based on the complex ab initio theory, it has been shown that Fröhlich's effective attractive electron-electron interaction term represents correction to electron correlation energy at transition from adiabatic into antiadiabatic state due to EP interactions. It has been shown that increased electron correlation is a consequence of stabilization of the system in superconducting electronic ground state, but not the reason for its formation.     

Hyperfinite Dimensional Representations of Spaces and Algebras of Measures

Let X be a locally compact topological space and (X, E, X_ω) be any triple consisting of a hyperfinite set X in a sufficiently saturated nonstandard universe, a monadic equivalence relation E on X, and an E-closed galactic set X_ω ⊆ X, such that all internal subsets of X_ω are relatively compact in the induced topology and X is homeomorphic to the quotient X_ω/E. We will show that each regular complex Borel measure on X can be obtained by pushing down the Loeb measure induced by some internal function X ? ^*\Bbb CX \rightarrow {}{^{\ast}{\Bbb C}} . The construction gives rise to an isometric isomorphism of the Banach space M(X) of all regular complex Borel measures on X, normed by total variation, and the quotient M_w(X)/M₀(X){\cal M}_{\omega}(X)/{\cal M}_0(X) , for certain external subspaces M₀(X), M_w(X){\cal M}_0(X), {\cal M}_{\omega}(X) of the hyperfinite dimensional Banach space ^*\Bbb C^X{}{^{\ast}{\Bbb C}}^X , with the norm ‖f‖₁ = ∑_{x ∈ X} |f(x)|. If additionally X = G is a hyperfinite group, X_ω = G_ω is a galactic subgroup of G, E is the equivalence corresponding to a normal monadic subgroup G₀ of G_ω, and G is isomorphic to the locally compact group G_ω/G₀, then the above Banach space isomorphism preserves the convolution, as well, i.e., M(G) and M_w(G)/M₀(G){\cal M}_{\omega}(G)/{\cal M}_0(G) are isometrically isomorphic as Banach algebras.     

Superconductivity and the effective electron–electron interaction mechanism in the light of the configuration interaction study

The effect of electron–phonon interactions, described by the effective electron–electron interaction mechanism, on the electronic structure of molecular systems has been investigated by the configuration interaction method. For systems with strongly quasi-degenerate electronic states near to the Fermi surface, this interaction mechanism, according to the BCS theory, results in the electronic ground-state energy lowering and in the gap formation. A more rigorous treatment of the configuration interaction method as applied in this paper confirms the electronic ground-state energy lowering, but the obtained results indicate that the effective electron–electron interaction term does not yield the experimentally detected temperature dependence of the gap. Accordingly, the two-particle mechanism seems not to be the key factor for the gap formation and for the microscopic mechanism of superconductivity, which agrees with the results of the molecular nonadiabatic theory of electron–vibrational interactions.     

Preparation of Boc-Amino-Acid or Peptide Aldehydes via Reduction of Corresponding Phenyl Esters

A new alternative method for the preparation of amino-acid and peptide aldehydes based on reduction of corresponding phenyl esters with lithium tri(tert-butoxy)aluminium hydride is described.     

Some Ramsey-type theorems for countably determined sets

 Let X be an infinite internal set in an ω¹-saturated nonstandard universe. Then for any coloring of [X] ^k , such that the equivalence E of having the same color is countably determined and there is no infinite internal subset of [X] ^k with all its elements of different colors (i.e., E is condensating on X), there exists an infinite internal set Z⊆X such that all the sets in [Z] ^k have the same color. This Ramsey-type result is obtained as a consequence of a more general one, asserting the existence of infinite internal Q-homogeneous sets for certain Q ⊆ [[X] ^k ] ^m , with arbitrary standard k≥ 1, m≥ 2. In the course of the proof certain minimal condensating countably determined sets will be described. Received: 17 October 2000 / Published online: 12 July 2002