Patent ID: 6884868

Claim:
A polypeptide compound of the following general formula (I): wherein R 1 is hydrogen or acyl group, R 2 and R 3 are independently hydrogen; lower alkyl which may have one or more suitable substituent(s) selected from the group consisting of amino, carboxy, sulfinic acid group, sulfonic acid group, hydroxy(lower)alkylamino which may have hydroxy(lower)alkyl, hydroxysulfonyloxy, imino, lower alkoxy, oxo, lower alkylthio, cyano(lower)alkylidene, and heterocyclic group which may have one or more lower alkyl; lower alkoxycarbonyl which may have one or more suitable substituent(s) selected from the group consisting of lower alkanoyloxy and heterocyclic group; lower alkenyloxycarbonyl; ar(lower)alkoxycarbonyl; lower alkanoyl which may have one or more suitable substituent(s) selected from the group consisting of amino, hydroxy and heterocyclic group; heterocycliccarbonyl; mono or di(lower)alkylcarbamoyl; sulfonic acid group; heterocyclic group which may have one or more suitable substituent(s) selected from the group consisting of lower alkyl, hydroxy(lower)alkyl, carboxy(lower)alkanoyl which may have amino, heterocycliccarbonyl, cyclo(lower)alkyl, and oxo; lower alkylidene which may have mono or di lower alkylamino; carboxy(higher)alkyl or cyano, R 4 is hydrogen or hydroxy, R 5 is hydrogen, hydroxy, lower alkoxy or hydroxysulfonyloxy, and R 6 is hydroxy or acyloxy, or a salt thereof.