Yasuyuki Kurita

Two insecticidal monoterpenes, telfairine and aplysiaterpenoid A, from the red alga Plocamium telfairiae: Structure elucidation, biological activity, and molecular topographical consideration by a semiempirical molecular orbital study

Abstract Two insecticidal polyhalogenated monoterpenes, aplysiaterpenoid A and telfairine were isolated from the red alga Plocamium telfairiae. Both compounds showed strong insecticidal activities against the German cockroach (Blatella germanica) and mosquito larvae (Anopheles gambiae). The dieldrin-resistant strain of mosquito larvae (A. gambiae) which exhibited the significant cross-resistance to ( 1246 35 )-1,2,3,4,5,6- hexachlorohexane (γ-BHC) also revealed weak but definite cross-resistance to aplysiaterpenoid A and telfairine. The electrophysiological symptom that telfairine increases the frequency of spontaneous discharge and prolongs the synaptic after-discharge of the central nervous system of the German cockroach (B. germanica) in the same manner as γ-BHC indicated that telfairine also has some excitatory effect on the central nervous system. The molecular topographical studies by semiempirical molecular orbital calculation about these insecticidal monoterpenes were carried out in terms of their electrostatic similarity to picrotoxinin and extending volumes from the surface of picrotoxinin molecule. The result suggested that the orientations of the steric bulky regions and electronegative centers in aplysiaterpenoid A and telfairine could satisfy the geometrical requirement for interacting with the picrotoxinin receptor as well as γ-BHC, while the large extending volumes of both compounds led to the loose fitting into the receptor. Accordingly, we propose that two insecticidal monoterpenes from marine alga seem to interact with the picrotoxinin receptor, indicating that their mode of action is cyclodiene-type.

Decomposition analyses of the intermolecular interaction energies in two p-p stacking complexes: quinhydrone and N,N,N′, N′ -tetramethyl- p -diaminobenzene-chloranil complex

Although there is a similarity in the orbital interaction scheme between quinhydrone and N,N,N′,N′‐tetramethyl‐p‐diaminobenzene‐chloranil complex, the stacking conformations are different from each other. The former prefers the half‐stacked conformation, whereas the latter prefers the completely stacked conformation. We have done ab initio molecular orbital calculations and decomposition analyses of the intermolecular interaction energies to clarify the origin of the different stacking conformations. It was concluded that the main origin is the difference in the steric part of the interaction energies.

Secondary orbital interaction vs. orbital distortion in stereoselectivity

Abstract Stereoselectivities in reactions such as electrophilic additions to norbornene and 1-methoxycyclohexene-2, and reductions of cyclohexanone derivatives and a benzocycloheptenone one have been interpreted using frontier orbital theory. We concluded that the secondary orbital interaction is more important for the selectivities than the orbital distortion at the reaction center. This conclusion may be a motive for reexaminations of factors in stereoselectivities which could not be interpreted by the orbital distortion at the reaction center.

A simple method to display molecular orbitals with computer graphics

Abstract A computer program named LOBE was developed to draw molecular orbitals as lobes on a graphic display. With this program, any molecular orbital of large molecules can be displayed quickly. This program is suitable not only for general-purpose computers but also for microcomputers. A sample application is used to illustrate the program.

APPLICATIONS OF THE COMPUTER AIDED CHEMISTRY SYSTEM ACACS IN AGRICULTURAL CHEMICAL RESEARCH

We developed an interactive computer system for molecular design called ACACS through the joint cooperation with Sumitomo Pharmaceuticals Co., Ltd. and NEC Corporation. In the ACACS system, computer graphics is used to examine similarities in three-dimensional structure among compounds. We have used this system in research on various agrochemicals such as pyrethroid insecticides. We investigated similarities in molecular shape among several alcohol moieties of various ester type pyrethroids, and between ester and ether type pyrethroids, based on conformational analyses with molecular orbital methods. Furthermore, we presented a candidate for the active conformer of an ester type pyrethroid, esfenvalerate, based on conformational analyses and shape comparisons with low-activity pyrethroids.