Abstract: The compounds of this invention represented by the following formula: ##STR1## (wherein R is hydrogen atom, an alkyl group having C.sub.1 to C.sub.4, a hydroxy group or a halogen atom) can be obtained by condensing the compounds represented by the following formula: ##STR2## wherein R is as defined above, X is hydrogen atom, and Y is hydrogen atom or an amino protecting group or reactive derivatives thereof with (S)-arginine according to a method commonly employed in the peptide chemistry.The peptides according to this invention have strong inhibitory activity against aminopeptidase B, can raise immunity of the organisms and prove useful for inhibiting transfer of cancer and relapse thereof. Also, when used jointly with Bleomycin which is an antitumor agent, they can greatly enhance the antitumor effect of said agent.

Abstract: This invention provides the amino acid (2S,3R)-3-amino-2-hydroxy-4-phenylbutanoic acid which is prepared by hydrolysis of bestatin. Bestatin is a chemical which inhibits aminopeptidase B, leucine aminopeptidase and bleomycin hydrolase, enhances the antitumor effect of bleomycin, has the chemical name [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine, has the following structure ##STR1## and is prepared by cultivating a strain of streptomyces which produces bestatin in a nutrient medium under aerobic conditions until substantial activity inhibitory to aminopeptidase B is imparted to said cultured medium and then recovering said bestatin from said cultured medium. A preferred strain is Streptomyces olivoreticuli FERM-P No. 2590 (A.T.C.C. 31159).

Abstract: The present invention relates to new physiologically active peptides, derivatives thereof and a process for preparation thereof. In particular, it relates to new tetrapeptides designated amastatins A.sub.1, A.sub.2, A.sub.3, B.sub.1 and B.sub.2 and derivatives thereof which have an inhibitory effect on aminopeptidase A and also show stimulation of antibody formation and to a process for preparation thereof by cultivating a strain belonging to the genus Streptomyces.

Abstract: The present invention relates to new physiologically active peptides, derivatives thereof and a process for preparation thereof. In particular, it relates to new tetrapeptides designated amastatins A.sub.1, A.sub.2, A.sub.3, B.sub.1 and B.sub.2 and derivatives thereof which have an inhibitory effect on aminopeptidase A and also show stimulation of antibody formation and to a process for preparation thereof by cultivating a strain belonging to the genus Streptomyces.FIELD OF THE INVENTIONThe present invention relates to new physiologically active peptides, derivatives thereof and a process for preparation thereof. In particular, it relates to new tetrapeptides designated amastatins A.sub.1, A.sub.2, A.sub.3, B.sub.1 and B.sub.2 and derivatives thereof which have an inhibitory effect on aminopeptidase A and also show stimulation of antibody formation and to a process for preparation thereof by cultivating a strain belonging to the genus Streptomyces.

Abstract: A novel physiologically active peptide Val-X-Ala-X, in which X is 4-amino-3-hydroxy-6-methylheptanoic acid, which is prepared from R-Val-Val-X-Ala-X by the action of a microbial enzyme, N-acyl derivatives thereof which are produced by acylating said new peptide, and the processes for producing thereof and the microbial enzyme are disclosed.

Abstract: A novel physiologically active peptide Val--X--Ala--X, in which X is 4-amino-3-hydroxy-6-methylheptanoic acid, which is prepared from R--Val--Val--X--Ala--X by the action of a microbial enzyme, N-acyl derivatives thereof which are produced by acylating said new peptide, and the processes for producing thereof and the microbial enzyme are disclosed.

Abstract: This invention provides a new chemical named bestatin which inhibits aminopeptidase B, leucine aminopeptidase and bleomycin hydrolase, enhances the antitumor effect of bleomycin, has the chemical name [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine and has the following structure: ##STR1## and also provides a process for the production thereof which comprises cultivating a strain of streptomyces which produces bestatin in a nutrient medium under aerobic conditions until substantial activity inhibitory to aminopeptidase B is imparted to said cultured medium and then recovering said bestatin from said cultured medium. A preferred strain is Streptomyces olivoreticuli FERM-P No. 2590 (A.T.C.C. 31159).

Abstract: This invention provides a new chemical named bestatin which inhibits aminopeptidase B, leucine aminopeptidase and bleomycin hydrolase, enhances the antitumor effect of bleomycin, has the chemical name [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine and has the following structure: ##STR1## and also provides a process for the production thereof which comprises cultivating a strain of streptomyces which produces bestatin in a nutrient medium under aerobic conditions until substantial activity inhibitory to aminopeptidase B is imparted to said cultured medium and then recovering said bestatin from said cultured medium. A preferred strain is Streptomyces olivoreticuli FERM-P No. 2590 (A.T.C.C. 31159).

Abstract: A process for producing new pepstatins having anti-pepsin activity by cultivating a pepstatin producing strain in a nutrient medium containing assimilable carbon sources and nitrogen sources, and extracting the new pepstatins from the cultivated broth or medium.

Abstract: A process for producing pepstatins by means of a microorganism belonging to Streptomyces and producing pepstatins, wherein at least one amino acid selected from the group consisting of L-leucine, L-valine, L-alanine, L-aspartic acid, L-glutamic acid, and L-lysine is added to the reaction medium, which also contains an energy source.

Abstract: A trans isomer of 4-cyanoncyclohexane-1-carboxylic acid or its lower alkyl ester is reduced in a solvent in the presence of a hydrogenating catalyst, and hydrolyzing the produced ester in case the starting trans-isomer is a lower alkyl ester, then the trans-4-aminomethyl-cyclohexane-1-carboxylic acid is recovered from the reaction mixture.