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
Abstract
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.
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