Ipomeolides A and B, Resin Glycosides from Ipomoea pes-caprae and Combination Therapy of Ipomeolide A with Doxorubicin

摘要

Two new resin glycosides, ipomeolides A (1) and B (2), both with an unusual nonlinear heteropentasaccharide core, along with five known compounds were isolated from the n-hexane/CHCl3 (1:1) extract of the aerial parts of Ipomoea pes-caprae. Ipomeolides A (1) and B (2) are macrolactone analogues of the rare (11R)-jalapinolic acid, and macrolactonization occurred at C-2 of the second saccharide moiety. Compounds 1 and 2 show structural variation even in the pentasaccharide core. The structures of 1 and 2 were established by a combination of spectroscopic techniques as well as chemical modifications such as acetyl and acetonide derivatives as well as hydrolysis products. The new glycosidic acid was named ipomeic acid (1c). Compounds 1, 1b, and 2b were evaluated for cytotoxicity against human tumor cell lines. Compounds 1b and 2b were not effective on epithelial cells, but affected survival of K-562, which is of hematopoietic origin. A sublethal concentration of compound 1 (4 mu M) when used in combination with 1 mu M doxorubicin, an anticancer agent, significantly enhanced cytotoxicity to tumor cells. Such combined synergistic potency against leukemia cells and the absence of effects on epithelial cells may be beneficial for chemotherapy with minimal side effects to treat CML (chronic myeloid leukemia) malignancies.