Importance

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Abstract

A tetrapeptide derivative represented by the following formula or a salt thereof has a higher cyto-static activity than dolastatin 10, and is useful as an antitumor agent: ##STR1## wherein, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different and each represent a hydrogen atom, a lower alkyl group or an aralkyl group; Q represents ##STR2## or a group of --A.sub.2 --R.sub.7, wherein, A.sub.1 represents a direct bond or ##STR3## Y represents a hydrogen atom or --COR.sub.6, R.sub.5 represents a hydrogen atom, a lower alkyl group or an aralkyl group, R.sub.6 represents a hydroxyl group, a lower alkoxy group, an aralkyloxy group or ##STR4## wherein, R.sub.8 and R.sub.9 are the same or different and each represent a hydrogen atom, a lower alkyl group, a phenyl group or a 4- to 7-membered heterocyclic group containing one or two hetero atoms selected from S, O and N, or alternatively R.sub.8 and R.sub.9 may combine together with the nitrogen atom to which they are bonded to form a 4- to 7-membered heterocyclic ring optionally further containing one hetero atom selected from S, O and N, A.sub.2 represents a direct bond or a lower alkylene group, and R.sub.7 represents a cycloalkyl group, an aryl group or an indolyl group, provided that the case is excluded where both R.sub.1 and R.sub.2 represent isopropyl groups, R.sub.3 represents a sec-butyl group, R.sub.4 represents a methyl group, and Q represents an .alpha.-(2-thiazolyl)phenethyl group.

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First Claim