.alpha.-Aminoboronic acid peptides

A compound of the formula ##STR16## or a physiologically acceptable salt thereof, wherein A.sup.1 is an amino acid of L-configuration selected from the group consisting of Ala, Pro, Gly, Glu, Leu, Lys, Phe, Ser, Val, Ile, Arg, Tyr, Thr, Asp, Asn or Gln;

• A.sup.2 and A.sup.3 are, independently, amino acids of D or L-configuration selected from the group consisting of Ala, Arg, Asn, Asp, Cys, Gln, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr or Val;
• n is 1 and o is 0 or 1;
• R.sup.1 is --H or an N-terminal protecting group;
• R.sup.2 is an alkyl group of one to six carbons, optionally comprising an aromatic substituent, or one or more in-chain bivalent groups selected from the group consisting of --O--, --CO--, --S--, --NH--, --CONH--, --CH.dbd.CH-- or --SO.sub.2 --;
• and
• Y.sup.1 and Y.sup.2 are each --H, or taken together form a moiety derived from a dihydroxy compound having at least two hydroxy groups separated by at least two connecting atoms in a chain or ring, said chain or ring comprising carbon atoms, and optionally, a heteroatom or heteroatoms which can be N, S, or O;
• with the proviso that where is O, R.sup.1 cannot be --H.