Delphinidin (chloride) is an anthocyanidin, a natural plant pigment which serves as the precursor of certain anthocyanins that provide the blue-red colors of flowers, fruits, and red wine.[1] Delphinidin induces the release of nitric oxide by vascular endothelium, causing vasorelaxation.[2] It also inhibits signaling through epithelial growth factor receptors, suppressing the expression of estrogen receptor α and inducing both apoptosis and autophagy at a dose of 1-40 μM.[3],[4] Delphinidin also inhibits the histone acetyltransferase activities of p300/CBP (IC50 = ~ 30 μM).[5]

Reference:
[1]. Holton, T.A., Brugliera, F., Lester, D.R., et al. Cloning and expression of cytochrome P450 genes controlling flower colour. Nature 366, 276-279 (1993).
[2]. Andriambeloson, E., Magnier, C., Haan-Archipoff, G., et al. Natural dietary polyphenolic compounds cause endothelium-dependent vasorelaxation in rat thoracic aorta. Journal of Nutrition 128, 2324-2333 (1998).
[3]. Ozbay, T., and Nahta, R. Delphinidin inhibits HER2 and Erk1/2 signaling and suppresses growth of HER2-overexpressing and triple negative breast cancer cell lines. Breast Cancer 5, 143-154 (2011).
[4]. Aiyer, H.S., Warri, A.M., Woode, D.R., et al. Influence of berry polyphenols on receptor signaling and cell-death pathways: Implications for breast cancer prevention. Journal of Agricultural and Food Chemistry 1-16 (2012).
[5]. Seong, A.R., Yoo, J.Y., Choi, K.C., et al. Delphinidin, a specific inhibitor of histone acetyltransferase, suppresses inflammatory signaling via prevention of NF-κB acetylation in fibroblast-llike synoviocyte MH7A cells. Biochemical and Biophysical Research Communications 18(1), 581-586 (2011).