3,704,246 United States Patent Office Patented Nov. 28, 1972 2 (I) R 3,704,246 AMNO ACD DERVATIVES ( CH).--N Miklos Bodanszky, Shaker Heights, Ohio, assignor to R2-C YoH-R E. R. Squibb & Sons, Inc., New York, N.Y. No Drawing. Continuation-in-part of application Ser. No. R-i-o-c6 798,790, Feb. 12, 1969, which is a continuation-in-part wherein R is the residue of an a-amino acid, R1 is hydro of abandoned application Ser. No. 451,609, Apr. 28, gen, lower alkyl, hydroxy-substituted lower alkyl, or 1965. This application Dec. 16, 1970, Ser. No. 98,924 lower alkyl lower alkoxy; R and R3 each is hydrogen, int. C. C07d 87/54 lower alkyl, hydroxy-substituted lower alkyl, lower alkyl U.S. C. 260-333 9 Claims 10 lower alkoxy, or R and R3 together with the carbons to which they are joined form a phenyl ring which may be unsubstituted or substituted by halogen or nitro, and m ABSTRACT OF THE DESCLOSURE is an integer from 0 to 3. New lactone intermediates useful in the synthesis of 5 DETAILED DESCRIPTION OF THE INVENTION peptides are prepared by reacting an a-amino acid with Any a-amino acid may be treated according to this an active carbonyl compound which forms a Schiff's base. invention. This includes the naturally occurring ox-amino The latter is treated with a condensing agent so that acids see for example, Hackh's Chemical Dictionary, cyclization occurs and a lactone is formed from which a 3rd ed. (1944), pages 44-45 as well as synthetic ox peptide may be produced by reaction with an amino acid 20 amino acids. Some examples are monoaminocarboxylic ester removal of the protecting groups. aliphatic acids, e.g., glycine, a-aminoheptylic acid, o aminocaprylic acid, a-aminononylic acid, a-aminodecylic acid, a-aminoundecylic acid, alanine, serine, cysteine, threonine, methionine, valine, leucine, isoleucine; aro This application is a continuation-in-part of copending 25 matic monoaminomonocarboxylic acids, e.g., phenylala application Ser. No. 798,790, filed Feb. 12, 1969, now nine, tyrosine, dihydroxyphenylalanine, 3,5-dibromotyro abandoned, which in turn is a continuation-in-part of sine, 3-iodotyrosine, 3,5-diiodotyrosine, 3,5,3'-triiodo application Ser. No. 451,609, filed Apr. 28, 1965, now thyronine, and thyroxime; monoaminodicarboxylic acids abandoned. and their amides, e.g., aspartic acid, glutamic acid, aspar This invention relates to new intermediates useful in 30 agine and glutamine; diaminomonocarboxylic acids, e.g., the synthesis of peptides. More particularly, the invention lysine, hydroxylysine, ornithine and arginine; heterocyclic relates to amino acid derivatives, especially derivatives amino acids, e.g., histidine, tryptophane, proline, hy of a-amino acids, which are simultaneously protected and droxyproline, thiolhistidine; diaminocarboxylic acids, e.g., activated for reaction with other amino acids in the syn cystine, lanthionine and djenkolic; as well as cc-amino thesis of peptides. 35 acids of the same type found in special sources, e.g., In the usual synthesis of peptides, two amino acids are phenylglycine, butyrine, citrulline, homocystine, hypo joined "head to tail,” i.e., the carbonyl group of the acid glycin A, S-methylcysteine sulfoxide, allin and canava moiety of one amino acid is joined to the amino group of C. the second amino acid. It is conventional in such a syn 40 Other amino acids are aminomalonic acid, o-amino thesis to protect the reactive amino group of one amino adipic acid, oz-aminopimelic acid, oz-aminosuberic acid, acid with a readily removable protective group such as oz-aminosebacic acid, 5-hydroxyaspartic acid, cystine-6,6- a benzyloxycarbonyl, t-butyloxycarbonyl, phthalyl, tosyl dicarboxylic acid, 3-hydroxyglutamic acid, (3-methylaspar group, etc., so that the amino group does not enter into tic acid, 6-methyl-6-hydroxyaspartic acid, 8-methylglu the reaction. Then the carbonyl group of the same amino 45 tamic acid, (3,6-dimethylaspartic acid, y-hydroxyglutamic acid is activated with another group, e.g., with an azide acid, 6,y-dihydroxyglutamic acid, 6-phenylglutamic acid, or with an ester group such as the p-nitrophenyl ester, so ty-methyleneglutamic acid, oz-aminotricarballyic acid, 3 that the carbonyl group will react with or actylate the aminoalanine, y-aminobutyrine, homoarginine, homo amino group of the second amino acid in the presence of citrulline, o,a'-diaminosuccinic acid, c,c'-diaminoglutaric the protecting group. 50 acid, a,c'-diaminoadipic acid, oz,a'-diaminopimelic acid, This procedure, it is evident, requires two distinct re o,a'-diamino-3-hydroxypimelic acid, a,c-diaminosuberic actions with two separate compounds in preparation of acid, or,a'-diaminoazelaic acid, cz,a'-diaminosebacic acid, the one amino acid for the ultimate reaction with the c,c'-diaminodecanedicarboxylic acid, c,c'-diaminododec second amino acid. It further requires the combination of anedicarboxylic acid, y-methylproline, pipecolic acid, two proper groups which will give the desired protection 55 baikiain, 5-hydroxypipecolic acid, azetidine-2-carboxylic and activation of the particular amino acid involved. acid, 6-phenylserine, canaline, y-oxalysine, y-hydroxy ornithine, and 2-hexosaminic acids. A comprehensive dis BRIEF SUMMARY OF THE INVENTION cussion of amino acids, including those mentioned above is to be found in Chemistry of the Amino Acids, Green It has now been found that cy-amino acids can be both 60 stein et al., vol. III, Wiley, 1961. Other amino acids in protected and activated by reacting the amino acid with a addition to those listed are to be found in this volume but single compound and then forming a lactone. This method for sake of brevity are not specifically mentioned herein, and the novel lactones formed thereby form the essence but are included by reference. It is to be understood that of this invention. These lactones readily react with ce the present invention is applicable to any amino acid. amino acid esters to form condensation products from 65 The amino acid of the formula which the protecting-activating moiety is readily removed to leave the desired peptide. NH, Briefly, the method comprises reacting an a-amino acid R-CE-CO2H with an active carbonyl compound which forms a Schiff's wherein R is the residue of the amino acid is reacted with base and then the Schiff's base is treated with a condens 70 a carbonyl compound to produce a Schiff's base. These ing agent to induce cyclization and yield a lactone of the carbonyl compounds are aldehydes or ketones having the formula structural formula 3,704,246 4. wherein R is hydrogen, halo, especially chloro or bromo, or nitro, and n is 1, 2 or 3. Most preferred are salicyl aldehydes having a nitro or chloro group with the sub stituent meta or para but especially meta to the aldehyde group. The amino acid is reacted with the aldehyde or ketone in an inert Solvent, preferably an inert organic solvent wherein R is hydrogen or a straight or branched chain such as dimethylformamide, dioxane, pyridine or the like lower alkyl radical of from 1 to 4 carbon atoms; R and under conventional conditions for forming a Schiff's base. Reach is hydrogen, a lower alkyl radical, a hydroxy O Then, after the Schiff's base has formed, without isolating substituted lower alkyl radical, a lower alkyl lower alkoxy the base unless desired, a condensing agent is added to radical, each of said radicals being straight or branched the reaction mixture to form the lactone. An alcohol may chain of from 1 to 4 carbon atoms; R and R3 taken also be used as the reaction medium in which the Schiff's together with the carbon atoms to which they are joined base is formed, but in this case the solvent must be re are a phenyl ring which may be unsubstituted or which 5 moved before adding the condensing agent. may be substituted by halogen or nitro; m is an integer Any condensing agent which promotes the formation from 0 to 7 when the carbonyl compound is aliphatic of acyl esters may be used. These include, for example, and an integer from 0 to 3 when the carbonyl compound dicycloalkylcarbodiimides, e.g., dicyclohexylcarbodiimide; is aromatic. dialkylcarbodiimides, e.g., dipropylcarbodiimide; diaryl 20 carbodiimides, e.g., diphenylcarbodiimide; alkoxyacetyl Examples of suitable aliphatic carbonyl compounds are enes, e.g., ethoxyacetylene, diphenylketene, etc. Dicyclo the enol forms of the following compounds: hexylcarbodiimide and ethoxyacetylene are preferred. malondialdehyde About one mol or more of condensing agent per mol of 3-ketobutyra Schiff's base may be used. A mol ratio of about 1:1 may succindialdehyde 25 be used when the condensing agent is a carbodiimide. 4-ketopentanal An excess of the condensing agent is preferable when glutardialdehyde other condensing agents are used. 2,4-pentanedione Sufficient time must elapse for the Schiff's base to form 4-ketohexanal before the condensing agent is introduced. The time period adipdialdehyde 30 may vary within rather broad limits depending upon the 2,4-hexanedione particular reactants, but a period of about one hour to 2,5-hexanedione about twenty-four hours is generally adequate. Stirring 2-methyl-3-ketopentanal and/or heating will of course accelerate the reaction. 2-methyl-4-ketopentanal Temperatures in the range of about 15 to 60° C. may 3-methylpentanedial 35 be used. 2-ethylsuccindialdehyde The cyclization reaction which occurs upon addition 3-methyl-2,4-pentanedione of the condensing agent must be effected in an anhydrous 2,4-heptanedione medium and the solvent must be one which has no reac 2-methyl-3,5-hexanedione tive hydroxy or carboxy group. Media such as those 2-methyl-4-ketohexanal 40 named above, except alcohols, may be used for the cy 3-methyl-2,4-hexanedione clization as well.