Studies on Rubia akane(RA) derivatives. Part 8. Design, syntheses and antitumour activity of cyclic hexapeptide RA analogues possessing an alkyl substituent on the Tyr-3 aromatic ring
Studies on Rubia akane(RA) derivatives. Part 8. Design, syntheses and antitumour activity of cyclic hexapeptide RA analogues possessing an alkyl substituent on the Tyr-3 aromatic ring
The effective conversion of RA-VII 1 into the naturally less-accessible RA-II 4 has been devised through boron tribromide bis-O-demethylation and successive selective partial O-methylation using diazo(trimethylsilyl)methane. The O-triflate 11 prepared from RA-II 4 was subjected to cross-coupling reaction with alkylstannanes to produce analogues 12, 13 and 15, while compounds 13 and 15 were later converted into analogues 14 and 16, respectively. Analogues 12–16 showed antitumour activity against P-388 leukaemia both in vitro and in vivo.
aromatic ring substituent modified RA derivatives were prepared from RA-VII (1), RA-V (8) and RA-II (11), and evaluated for cytotoxicity against P388 leukemia and KB cells. In terms of IC50 values, the C zeta methoxyl group of Tyr-3 greatly influenced the activities, while the substituents at the C zeta position of Tyr-6 were less important. One of the derivatives, Tyr-6-C zeta-deoxyRA-V (9, P388, IC50