D-proline is an isomer of the naturally occurring amino acid L-Proline. D-amino acids have been found in relatively high abundance in human plasma and saliva. These amino acids may be of bacterial origin but there is also evidence that they are endogenously produced through amino acid racemase activity.

Pendulone could be a valuable chemopreventive agent, it shows strong inhibition on the effect of the cell cycle induced by TPA and shows potent anti-tumor-promoting activity for an in vivo two-stage carcinogenesis test.

CDDO-2P-Im, an analog of CDDO-Imidazolide, has a chemopreventive effect. It can reduce the size and severity of the lung tumors in the mouse lung cancer model.