On the anti-Kekulé number of leapfrog fullerenes

The Anti-Kekulé number of a connected graph G is the smallest number of edges that have to be removed from G in such way that G remains connected but it has no Kekulé structures. In this paper it is proved that the Anti-Kekulé number of all fullerenes is either 3 or 4 and that for each leapfrog fullerene the Anti-Kekulé number can be established by observing finite number of cases not depending on the size of the fullerene.     

The number of Kekulé structures of polyominos on the torus

Let G be a (molecule) graph. A perfect matching, or Kekulé structure of G is a set of independent edges covering every vertex exactly once. Enumeration of Kekulé structures of a (molecule) graph is interest in chemistry, physics and mathematics. In this paper, we focus on some polyominos on the torus and obtain the explicit expressions on the number of the Kekulé structures of them.     

Directed tree structure of the set of kekulé patterns of polyhex graphs

A theorem is established revealing the structure of the set of Kekulé patterns of benzenoid hydrocarbons. This is a generalization of a previous result by Ohkami, Motoyama, Yamaguchi, Hosoya and Gutman.     

On the number of kekulé structures of unbranched cata-condensed benzenoid chains

It is known that an alternative algorithm to the Gordon-Davidson algorithm for counting the Kekulé valence structures of catacondensed non-branched benzenoid hydrocarbons is a reformulation of the original algorithm.     

Synthesis of novel sugar-lactam conjugates using the Aubé reaction

An efficient and convenient method for the synthesis of sugar-lactam conjugates is reported starting from readily available sugar azides using the Aubé reaction. Cyclic azido alcohols are used in the Aubé reaction for the first time in a carbohydrate setting. The resulting glycoconjugates could be further used to increase the chemical diversity on the sugar backbone, and may find potential applications as glycomimetics, peptidomimetics, in glycotargeting and in CNS drug delivery.     

On the number of Kekulé structures in capped zigzag nanotubes

Two theoretical formulae for the number of Kekulé structures in general capped zigzag nanotubes are established: one of which is by using the techniques of the transfer matrices, the other involves the eigenvalues of the transfer matrix which reveals the asymptotic behaviour of this index. In effective, according to the symmetric aspect of the tubule, the order of the transfer matrix could be notably decreased. As an application, the closed expressions for four types are given out and the relevant numerical results for those of length up to 50 are listed.     

Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate

Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev…     

Construction of the Skeleton of Phthalascidin,Mechanism of the Formation o the Key Tricyclic Lactam Intermediate

The mechanism of the formation of a key tricyclic lactam intermediate 3 was studied. It was found that the E-form compound 3 was transformed from the Z-form compound 4. The formation of 4 was a kinetically controlled process while the formation of 3 was a thermodynamically favorable one. A possible mechanism was given in this paper.     

Anionic polymerization of ϵ-caprolactam-lix effect of the ratio of reacting components,of the medium and of the ring size on the initial stage of the anionic polymerization of lactams

Effects of the concentrations and ratio of reacting components and of temperature on the kinetics of reaction of N-propionyllactam (I) with potassium salt of lactam (KL) were studied for derivatives of ϵ-caprolactam, 8-octanelactam and 12-dodecanelactam. For ϵ-caprolactam, the initial rates of propagation, acylation of open-chain amide groups and condensation of growth centres were estimated. At the ratio of the starting components [I]₀/[KL]₀ = 0.5-3, the participation of the polymerization reaction is constant, amounting to ca 45% of the overall consumption of 1. The condensation reaction is 14–36% of the total consumption of I; its initial rate passes through a maximum at [I]₀/[KL]₀ = 2. With increasing permittivity of the medium, the total rate of consumption of I increases; in two media with the same bulk permittivity, however, the rates may differ by as much as one order of magnitude.