| Research Abstract |
The purposes of this project is to develop new algorithms useful for the computational investigation of the multi-minimum problem in conformational analysis, to perform coding, and to apply the programs to the practical problems.
By the end of the proposed term of project, all these purposes have been achieved.
An entirely new algorithm, called Corner Flapping, for systematically generating all possible ring conformations was developed. It is likely that this algorithm will be the fastest of all the existing methods. The second version of the program CONFLEX2 for the execution of Corner Flapping has been deposited in public domain (QCPE #592, JCPE #21). An expanded modification of this algorithm, CONFLEX3, is almost ready at the time of writing this report. In addition, Karplus equation was extensively modified and a program for executing the multiparametric equation, 3JHHM, has been deposited in public domain (QCPE #591, JCPE #12).
These computational tools have been applied to a number
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of problems encountered in experimental organic chemistry. Surprisingly large number of new conformers have been found with CONFLEX2 for tricyclo[9.3.1.0^<3.8>]pentadecane, parent skeleton of the noted natural product taxin. Active conformations of sericornine, a sex pheromone for tobacco leaf bugs, have been estimated based on a large number of energy-minimum conformers obtained by CONFLEX2. An important 16-membered ring intermediate in the synthesis of Leuconolide A was subjected to CONFLEX2 in order to obtain thermodynamically significant conformations. This large scale calculation was successfully completed, and thus opened a door to attacking similar problems, such as the analysis of Woodward's lactone closure reaction in the total synthesis of erythromycin. Finally, we are interested in determining three-dimensional structure of natural products by the combination of modified Karplus equation, 3JHHM and MM. The methodology was developed using peracetates of small aiditols as models. A success rate of 92% has so far been achieved. Less
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