Abstract
Abstract A novel modulator of multidrug resistance (MDR) in tumor cells, kendarimide A ( 1 ), was isolated from an Indonesian marine sponge of Haliclona sp. Compound 1 reversed MDR in KB-C2 cells mediated by P-glycoprotein (P-gp) at a 6 μM concentration, and the chemical structure of 1 was characterized to be a linear peptide composed of N-methylpyroglutamic acid (pyroMeGlu), N-methylated eight-membered cysteinyl-cysteine (ox-[MeCys-MeCys]) together with many N-methyl amino acid residues. The amino acid sequence of 1 was determined by 2D NMR and FAB MS analysis. The absolute configuration of the amino acid residues in 1 except for the MeCys part was determined to be l -form respectively, based on interpretation of the HPLC analysis of Marfey's derivatives of the hydrolysates of 1 and the synthetic method for the pyroMeGlu residue.
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