Tetrapeptides deriving from dalbaheptide antibiotics

A process for producing a tetrapeptide of the general formula (Ic):

• ##STR24## wherein:
• R and R.sub.0 each independently represent amino or a protected amino group;
• R.sub.1 represents hydrogen or a protecting group of the carboxylic function;
• R.sub.2 is hydrogen;
• R.sub.3 is hydrogen or chloro;
• R.sub.4 is hydrogen or chloro;
• R.sub.5 is hydrogen;
• R.sub.6 is hydrogen or hydroxy;
• Y represents a carboxylic group or a functional derivative thereof, wherein said functional derivative is a carboxyester, a carboxamide or a substituted carboxamide;
• the phenolic hydroxy groups may optionally be protected;
• or its salts with acids and bases as well as its inner salts;
• which comprises:
• i) selectively protecting the free amino groups and the phenolic hydroxy groups of a pentapeptide of the formula (IIIc);
• ##STR25## wherein:
• T represent amino, alkylamino or a protected amino group from which the original amino group can be readily restored, and Y, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are as defined above, and its salts with acids and bases as well as its inner salts;
• ii) oxidizing the hydroxymethyl moiety of the selectively protected pentapeptide to carboxy, yielding a compound of formula (IVc) ##STR26## wherein T, Y, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 have the same meanings as above;
• iii) deprotecting the amino and, optionally, the phenolic hydroxy groups of the compound of formula (IVc), and;
• iiii) submitting the above deprotected compound to a double Edman degradation and, optionally, protecting the free amino groups and the carboxylic rests of the resulting compound.