Computational Study on the Conformations of Gambogic Acid.

The conformations of gambogic acid were studied using force fields, MM3*, AMBER*, MMFFs and OPLS2005, and B3LYP methods. In a model molecule, only the MM3* and AMBER* methods produced the same number of conformers as B3LYP, generating two conformations for rings 1 and 2, and a single conformation for rings 3 and 4. The preferred conformations of these rings are maintained in a conformer of the actual gambogic acid generated using the AMBER* and B3LYP methods. Although this calculated conformer matches well with the crystal structure, it shows that H43, C25=C26 and C30=C31 bonds may be misassigned in the crystal structure.