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, C25C26 and C30C31 bonds may be misassigned in the crystal structure.