Method of manufacturing polyamino acid with microwaves

Homopolyamino acids and copolyamino acids are prepared by polycondensation of one kind or a mixture of two or more kinds of monoammonium, diammonium, monoamide, diamide or monoamideammonium salts of malic acid and/or maleic acid and/or fumaric acid, one kind or two or more kinds of amino acid being added to said raw materials, respectively, with application of microwaves, the resulting polyamino acids (imide type) being converted to peptide type, homopolyamino acids and copolyamino acids, respectively upon partial hydrolysis. The operation involved in the reaction is simple and the method permits the use of low cost reaction materials. As a result, imide type and also peptide type, homopolyamino and copolyamino acids are produced with uniform quality at a high rate of yield within an extremely short period of time. Accordingly, the method is incomparably superior to those which have been announced in the past.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is related to making improvements in synthesizing 
homopolyamino acids or copolyamino acids. 
b 2. Description of the Prior Art 
Synthetic polyamino acids as protein model compounds are considered 
important as "biopolymers". Accordingly, applications in the industrial 
sector have become very active within the past years. 
These synthetic amino acids have attracted attention as polymers for fixing 
useful bacterium and enzymes, carriers of fixing chemicals, special 
bonding materials, gas permeable membrane, antithrombus agents, foundation 
for cosmetics, skin covering materials, synthetic leather, ion exchange 
resins, chelating agents, foaming agents, fibers and various types of 
films. 
Conventional methods of obtaining polyamino acids are given below. (1) The 
well known method of directly heating and polycondensing amino acids 
[Ann., 157, 24, (1871); J.C.S., 851 (1953); J.A.C.S., 80 , 3361 (1958); 
J.A.C.S., 80, 2694 (1958); J.A.C.S., 82, 3745 (1960)]. (2) Method of 
decarboxylation polymerization by using N-carboxyl acid anhydride (NCA) of 
amino acid [J.A.C.S., 79, 3961 (1957); J. Poly. Sci., A5, 2867 (1967); J. 
Poly. Sci., A14, 2065 (1976); Japanese Patent Publication Nos. 1967 
(42)-20793 and 1971 (46)-27828]. (3) Method of polymerizing activated 
amino acid ester [Japanese Patent Public Disclosure (Laid-Open 
Publication) No. 1979 (54)-47799; J. Macromol, Sci. Chem., A15, 999 
(1981); Khim, Prir. Soedin, 773, (1973)]. (4) Method of polymerizing 
N-dithiocarbonylalcoxylcarbonyl amino acid by heating [Japanese Patent 
Publication No. 1970 (45)-9391]. (5) Method of polymerizing acid chloride 
hydrochloride of amino acid (DOS 2364152). 
However, obtaining polyamino acid by Method (1) aforementioned has 
disadvantages due to thermal decomposition of starting materials and 
formation of diketopiperazine, a byproduct formed by cyclization of 
dipeptide. Method (2) is widely used at present, but it has the 
disadvantage of using toxic phosgene in addition to problems brought about 
by the fact that NCA is unstable especially in relation to moisture and 
that it is difficult to manufacture the substances in large quntities. In 
methods mentioned above other than Method (1), the high production costs 
of the methods are prohibitive in terms of practical use. 
The inventor has been successful in inventing a method of obtaining 
copolyamino acids [Japanese Patent Application No. 1984 (59)-60160] by 
mixing ammonium salts or amide of malic acid, fumaric acid and maleic acid 
with amino acid and heating the mixture in an oil bath to promote easy 
polycondensation. 
Microwave is used widely in radar and other communication facilities and it 
is also making a major contribution in spectroscopy in the physical and 
chemical sectors. It is also used in household electronic ranges. However, 
microwave is rarely used for chemical reactions. Some of the typically 
rare examples are crosslinking polyurethane and plyester [RGE, Rev. Gen. 
Electr., 826, (1981)], polymerization of difluoroethylene [Eur. Polym., 
J., 15, 265, (1979)], manufacture of bonding agents [Japanese Patent 
Public Disclosure (Laid-Open Publication) No. 1978 (53)-109535], and 
manufacture of polyurethane foam (U.S. Pat. No. 3,294,879). 
As mentioned above, there are disadvantages in the conventional methods of 
manufacturing polyamino acids such as unstable starting monomers, high 
prices, or complicated proceses. Furthermore, the method covered by 
Japanese Patent Application No. 1984 (59)-60160 is handicapped by 
requiring a comparatively long reaction time. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a method of manufacturing 
homopolyamino acids and copolyamino acids having excellent quality at high 
yield in an extremely short reaction time. 
Other objects and advantages of this invention will become apparent to 
those skilled in the art by reference to the detailed description of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The method of manufacturing a homopolyamino acid (imide) is characterized 
by polycondensation of one kind or a mixture of two or more kinds of 
monoammonium, diammonium, monoamide, diamide or monoamideammonium salts of 
malic acid and/or maleic acid and/or fumaric acid, with application of 
microwaves. 
The method of manufacturing a copolyamino acid (imide) is characterized by 
copolycondensation of one kind or a mixture of two or more kinds of 
monoammonium, diammonium, monoamide, diamide or monoamideammonium salts of 
malic acid and/or maleic acid and/or fumaric acid with the addition of one 
kind or two or more kinds of amino acid with application of microwaves. 
The resulting homopolyamino acid (imide) and copolyamino acid (imide) are 
converted to corresponding peptide, homopolyamino acid and copolyamino 
acid upon partial hydrolysis at pH 5-12. 
As to the microwaves, 1000 MHz to 1000 KMHz used, but 2000 to 3000 MHz is 
more preferable. 2450 MHz can be used for the sake of convenience with 
electronic ranges. It is desirable to use microwaves under nitrogen 
atmosphere for irradiation. A period of several seconds to a few hours is 
generally sufficient as the exposure time. 
Working pressure is acceptable under normal pressure, if water produced 
from the condensation reaction is discharged from the system. The pressure 
of the system can be reduced to remove the water thoroughly. Furthermore, 
azeotropic dewatering can be employed. The polycondensation reaction is 
sufficiently promoted without the use of catalysts, but pyrosulfuric acid, 
phosphonates, phosphites, phosphoric acid, sulfonic acids, quanternary 
ammonium salts and the like can be used as condensation catalysts and 
co-use of solvents is allowed as long as they do not fundamentally impede 
the progress of the reaction. 
The amino acids mentioned herein are referred to as .alpha.-, .beta.-, 
.gamma.-, .delta.- and .epsilon.-amino acids. Namely, neutral 
.alpha.-amino acids such as glycin, alanine, phenylalanine, leucine, 
isoleucine, valine, methionine, cystine, cysteine, serine, and threonine; 
acidic .alpha.-amino acids such as aspartic acid, glutamic acid, 
.alpha.-aminoadipic acid, aminomalonic acid, .alpha.-aminopimelic acid, 
.alpha.-aminosebacic acid, .beta.-methyl-glutamic acid, and 
.beta.,.beta.-dimethylaspartic acid; free and partial salts of basic 
.alpha.-amino acids such as ornithine, lysine, arginine and histidine; 
.beta.-amino acids such as .beta.-alanine, .beta.-phenylalanine, 
.beta.-amino butyric acid, .alpha.-methyl .beta.-aminopropionic acid, 
isoserine, .beta.-tyrosine, and taurine; .gamma.-amino acids such as 
.gamma.-amino butyric acid and its derivatives; .delta.-amino acids such 
as .delta.-amino valeric acid and its derivatives; .epsilon.-amino acids 
such as .epsilon.-amino caproic acid and its derivatives. The .gamma.-, 
.delta.-, or .epsilon.-amino acid derivatives are defined as ones which 
contain the .gamma.-, .delta.- or .epsilon.-amino acid structure in their 
molecula. 
Optically active or inactive amino acids may both be used for the 
production of copolyamino acids. The forms of the amino acids (L or D or 
DL) can be suitably selected in accordance with the intended applications 
of the production of copolyamino acids. 
Neutral or alkaline, partial hydrolysis of the polycondensed products 
(imide type) makes it easy to obtain peptide type, homopolyamino acids or 
copolyamino acids. 
The method used in the invention drastically shortens the reaction time, as 
compared with conventional methods using an oil bath as a means of 
heating, and the yield is high. Further, as compared with reaction by 
thermal conduction using an oil bath, a uniform reaction takes place 
internally and a more uniform polymer is obtained. This type of a reaction 
is much more advantageous in many aspects when carrying out large-scale 
production, especially from the energy standpoint. 
Accordingly, the operation involved in the reaction is simple and the 
method permits the use of low cost reaction materials. As a result, imide 
type and peptide type, homopolyamino and copolyamino acids are produced 
with uniform quality at a high yield within an extremely short period of 
time. Therefore, the method is incomparably superior to those which have 
been announced in the past. 
The reaction of obtaining anhydropolyaspartic acid (imide) and polyaspartic 
acid (peptide) from malic acid monoammonium salt is expressed as follows: 
##STR1## 
Explanations of the invention are given below in more detail by way of 
examples and the present invention is in no way restricted by them. 
EXAMPLE I 
2.0 grams each of malic acid monoammonium salt (referred to as "A"), maleic 
acid monoammonium salt (referred to as "B"), and ammonium salt of maleamic 
acid (referred to as "C") were put into a test tube and placed in an 
electronic range, Model No. RO-1700, manufactured by Mitsubishi Electric 
Co. (output: 500 W; frequency: 2450 plus/minus 50 MHz; oscillating tube: 
1035 W (10.35 A). Polycondensation was carried out by irradiating the 
mixture with microwaves for predetermined periods of time. 
The reactant was dispersed by addition of distilled water and the aqueous 
mixture was dialyzed for a period of 24 hours, using a cellophane 
dialyzing membrane (24 .ANG. pore). Then the mixture was freeze-dried to 
obtain the homopolymer (imide type). The yields are given in Table 1. 
The polymer thus obtained indicated negative in the ninhyrin test and the 
biuret test showed positive. Infrared absorption spectrum of the polymer 
indicated absorption near 1700 cm.sup.-1 and 1780 cm.sup.-1 indicating 
five-membered cylic imide of anhydropolyaspartic acid residue. 
The polymer was partially hydrolyzed by an aqueous solution of sodium 
bicarbonate. The solution was made acidic by adding 10% acetic acid and 
dialyzed and then freeze-dried. The product thus obtained showed strong 
absorptions of amide I 1650 cm.sup.-1 and of amide II 1550 cm.sup.-1, and 
exhibited absorption of carboxyl group near 1700 cm.sup.-1. 
Accordingly, it was found that the polymer obtained from polycondensation 
by microwaves was structurally anhydropolyaspartic (imide type), and the 
polymer was partially hyddrolyzed with aqueous sodium bicarbonate to 
obtain a peptide type homopolyamino acid (polyaspartic acid) having free 
carboxyl groups. 
The polymer obtained from plycondensation ("A", reaction time 45 minutes) 
was hydrolyzed with 6N-HCl at 110.degree. for 24 hours in a sealed tube 
under reduced pressure. Aspartic acid (86.1%) was detected with an 
automatic amino acid analyzer. 
TABLE 1 
______________________________________ 
Yields of homopolyamino acid obtained from poly- 
condensation of "A", "B" and "C" by microwaves 
Reaction Time "B" 
(min) "A" Yield (wt %) 
"C" 
______________________________________ 
15 32.6 -- -- 
30 38.6 51.1 43.1 
45 45.6 -- -- 
60 51.2 -- -- 
90 53.5 -- -- 
______________________________________ 
##STR2## 
EXAMPLE II 
Malic acid monoammonium salt "A" and one kind of various amino acids 
[Glycin (Gly), L-Alanine (L-Ala), L-Valine (L-Val), L-Glutamic Acid 
(L-Glu), L-Phenylalanine (L-Phe), L-Lysine-monohydrochloride (L-Lys-HCl)] 
were mixed at various mol ratios and processed as in the case of Example 
I. 
The copolyamino acids (imide type) thus obtained were placed in a sealed 
tube with 6N HCl and were hydrolyzed at 110.degree. C. for a period of 24 
hours under reduced pressure. The yields (wt %) of the copolymers and the 
amino acid compositions (mol %) of said copolyamino acid obtained by an 
automatic amino acid analyzer are shown in Table 2. The amino acid 
contents in the copolyamino acids are also higher than those obtained by 
using oil bath. 
For comparison, the yields of the copolyamino acids and the amino acid 
compositions obtained by heating with oil bath (all conditions were the 
same as Example I other than heating in an oil bath at 180.degree. C. for 
4 hours) are indicated in Table 2 in parentheses. 
A comparison of time course of the yields obtained by utilizing microwaves 
and an oil bath is shown in FIG. 1. As can be clearly seen, the time taken 
for reaction with microwaves is shorter and the polymer yields are higher. 
TABLE 2 
______________________________________ 
Yields of copolyamino acid obtained from 
mixtures of malic acid monoammonium salt ("A") 
and amino acid, and compositions of amino acid 
Amino Acid: "A" 
Yield Amino Acid Aspartic Acid 
(mol ratio) 
(wt %) (mol %) (mol %) 
______________________________________ 
Gly 41.4 (30.1) 
40.8 (34.3) 
59.2 (65.7) 
1:2 
L-Ala 16.5 (14.7) 
57.2 (42.6) 
42.8 (57.4) 
1:1 
L-Val 52.0 (31.5) 
70.6 (35.1) 
29.4 (64.9) 
1:1 
L-Glu 31.3 (33.1) 
18.4 (13.5) 
81.6 (86.5) 
1:2 
L-Phe 71.3 (64.9) 
51.3 (40.0) 
48.7 (60.0) 
1:2 
L-Lys--HCl 54.4 (48.1) 
42.2 (38.7) 
57.8 (61.3) 
1:2 
______________________________________ 
##STR3##