| prov:value
| - A peptide of the formulawhereinB.sub.1 is in the L- or D- configuration and is arginine, lysine, or lysine which is acylated by a protective group of the urethane type,B.sub.2 is arginine or lysine,A.sub.1 is in the L- or D- configuration and is phenylalanine, tyrosine, or tryptophan,A.sub.2 is phenylalanine, tyrosine, or tryptophan, andX is glutamine, glycine, proline, or arginine, or is an ester
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