Sweetening agent derived from L-aspartic or L-glutamic acid

The present invention relates to a novel sweetening agent and to its method of preparation. This novel sweetening agent is a 2-substituted acyl derivative of L-aspartic or L-glutamic acid and has the general formula ##STR1## R being an acyl group of the formula ##STR2## and R' being a group of the formula ##STR3## R.sub.1, R.sub.2, R.sub.3, X, Y and Z being variously defined. This novel sweetening agent is essentially characterized by a high sweetening potency and a high stability compatible with the conditions of industrial use, and is applied especially for sweetening soft drinks.

The present invention relates to a novel sweetening agent derived from 
L-aspartic or L-glutamic acid and to its method of preparation. 
This novel sweetening agent is particularly useful for sweetening a variety 
of products and in particular drinks, especially soft drinks, foods, 
confectionery, pastries, chewing gums, hygiene products and toiletries, as 
well as cosmetic, pharmaceutical and veterinary products. 
It is known that, to be usable on the industrial scale, a sweetening agent 
must possess firstly an intense sweetening potency, making it possible to 
limit the cost of use, and secondly a satisfactory stability, i.e. a 
stability compatible with the conditions of use. 
In the particular case of soft drinks, which represent the main use of 
sweetening agents, it is very difficult to obtain a satisfactory 
stability, all the more so because some of these drinks have the 
characteristic of being acid with a pH generally of between 2.5 and 3.5. 
The documents U.S. Pat. Nos. 3,725,453 and 3,775,460 have described 
sweetening agents derived from L-aspartic acid, of the following general 
formula: 
##STR4## 
in which X is CF.sub.3 or CCl.sub.3 and in which Y is 4-CN--C.sub.6 
H.sub.4, 4-Cl--C.sub.6 H.sub.4, 4-Br--C.sub.6 H.sub.4, 4-F--C.sub.6 
H.sub.4 or C.sub.6 H.sub.5. The sweetening potency of some of these 
compounds has been evaluated (J. Med. Chem., 1973, 16(2), p. 162-166). For 
example, the compound of formula (1) (X=CF.sub.3 and Y=4-CN--C.sub.6 
H.sub.4) has a sweetening potency equal to 3000 times that of sucrose (by 
comparison with a 2% solution of sucrose): 
##STR5## 
The compounds of general formula (A) in which X=CF.sub.3 and 
Y=4-Cl--C.sub.6 H.sub.4, 4-Br--C.sub.6 H.sub.4 or C.sub.6 H.sub.5 have a 
weaker sweetening potency than the compound of formula (1), which is 
between 12 and 120 times that of sucrose. 
Furthermore, it has been shown that the L-aspartyl residue in the above 
compounds can be replaced with its higher homolog, the L-glutamyl residue, 
without appreciable modification of the sweetening potencies 
(Naturwissenschaften, 1981, 68, 143). 
The document JP-A-87-132847 discloses in general terms sweetening agents of 
the general formula 
##STR6## 
in which X is CN or NO.sub.2 and n is equal to 1 or 2. The most active 
compound specifically described, of the formula 
##STR7## 
possesses a weak sweetening potency evaluated at 40 times that of sucrose. 
The document JP-A-87-132863 discloses in general terms sweetening agents of 
the general formula 
##STR8## 
in which X is CF.sub.3 CO or CCl.sub.3 CO, Y is H, halogen, CN or NO.sub.2 
and n is equal to 1 or 2, the asterisk indicating that the amino acid 
residue can have an L or DL configuration. Only two compounds are 
specifically described, which are derived from L-aspartic acid (n=1) and 
in which Y=H and X=CF.sub.3 CO and CCl.sub.3 CO, and their sweetening 
potencies are respectively 40 times and 1 times that of sucrose. 
The document JP-A-87-252754 discloses in general terms sweetening agents of 
the general formula 
##STR9## 
in which X is CN or NO.sub.2, R is H or a C.sub.1 -C.sub.10 alkyl, 
aromatic, alkoxy or aryloxy group and n is equal to 1 or 2, and in which 
the asterisk indicates that the amino acid residue has an L or DL 
configuration. 
Of the 15 Examples specifically described (Table 1), 14 compounds are 
derivatives of aspartic acid and only one is a derivative of glutamic 
acid. The sweetening potency (SP) of these compounds (by comparison with a 
5% solution of sucrose) is between 1 and 720 times that of sucrose. 
TABLE 1 
______________________________________ 
R * n X SP 
______________________________________ 
H L 1 CN 40 
H L 1 NO.sub.2 
1 
H D 1 CN 110 
H D 1 NO.sub.2 
50 
CH.sub.3 D 1 CN 10 
C.sub.6 H.sub.5 
L 1 CN 720 
C.sub.6 H.sub.5 
L 1 NO.sub.2 
420 
CH.sub.3 O L 1 CN 70 
CH.sub.3 O D 1 CN 140 
C.sub.2 H.sub.5 O 
L 1 CN 80 
C.sub.6 H.sub.5 O 
L 1 CN 90 
C.sub.6 H.sub.5 CH.sub.2 O 
L 1 CN 260 
C.sub.6 H.sub.5 CH.sub.2 O 
D 1 CN 110 
C.sub.6 H.sub.5 CH.sub.2 O 
D 1 NO.sub.2 
70 
C.sub.6 H.sub.5 CH.sub.2 O 
L 2 CN 2 
______________________________________ 
Among these compounds, the one possessing the highest sweetening potency 
(720 times that of sucrose) is derived from L-aspartic acid and has the 
formula 
##STR10## 
The only compound described which is derived from L-glutamic acid possesses 
a very weak sweetening potency of the order of 2 times that of sucrose, 
which excludes any possibility of industrial application. 
The document EP-A-0.338.946 has proposed a novel family of sweetening 
agents of the general formula 
##STR11## 
in which R is a saturated or unsaturated, acyclic, cyclic or mixed 
hydrocarbon group containing five to thirteen carbon atoms, R' is a 
4-cyanophenyl, 2-cyanopyrid-5-yl or 2-cyanopyrimidin-5-yl group and n is 
equal to 1 or 2. This document is illustrated by 25 Examples (Table 2). 
One of the preferred compounds in this document possess a sweetening 
potency of 1000 times that of sucrose and has the following formula: 
##STR12## 
TABLE 2 
______________________________________ 
R n R SP 
______________________________________ 
CH.sub.3 (CH.sub.2).sub.3 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
300 
CH.sub.3 (CH.sub.2).sub.4 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
600 
CH.sub.3 (CH.sub.2).sub.5 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
2000 
CH.sub.3 (CH.sub.2).sub.6 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
400 
CH.sub.3 (CH.sub.2).sub.2 CHCH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
200 
(CH.sub.3).sub.2 CHCH.sub.2 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
100 
c-C.sub.6 H.sub.11 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
200 
c-C.sub.6 H.sub.11 CH(CH.sub.3) 
1 4-CN--C.sub.6 H.sub.4 
200 
C.sub.6 H.sub.5 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
1000 
C.sub.6 H.sub.5 CH.sub.2 CH.sub.2 
1 4-CN--C.sub.6 H.sub.4 
300 
CH.sub.3 (CH.sub.2).sub.3 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
1500 
CH.sub.3 (CH.sub.2).sub.4 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
5000 
CH.sub. 3 (CH.sub.2).sub.5 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
7000 
CH.sub.3 (CH.sub.2).sub.6 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
2000 
(CH.sub.3).sub.2 CHCH.sub.2 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
800 
CH.sub.3 (CH.sub.2).sub.2 CH(CH.sub.3)CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
5000 
CH.sub.3 (CH.sub.2).sub.2 CH.dbd.CHCH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
3000 
CH.sub.3 CH.dbd.CHCH.dbd.CHCH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
2000 
C.sub.6 H.sub.5 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
20 
C.sub.6 H.sub.5 CH.dbd.CHCH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
2000 
C.sub.6 H.sub.5 CH(CH.sub.3)CH.sub.2 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
400 
c-C.sub.6 H.sub.11 CH.sub.2 CH.sub.2 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
7000 
C.sub.6 H.sub.5 CH.sub.2 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
300 
C.sub.6 H.sub.5 CH.sub.2 CH.sub.2 CH.sub.2 
2 4-CN--C.sub.6 H.sub.4 
800 
CH.sub.3 (CH.sub.2).sub.5 CH.sub.2 
2 2-CN-pyrid-5-yl 
4000 
______________________________________ 
Thus only a limited number of compounds described in the state of the art 
have an advantageous sweetening potency. 
Moreover, all these compounds have the major disadvantage, in terms of 
their use as sweetening agents, of having a poor stability in aqueous 
solution (i.e. under the normal conditions of use of synthetic sweetening 
agents), which considerably limits their application on the industrial 
scale or even makes it impossible. 
Thus the object of the present invention is to provide a novel family of 
sweetening agents, derived from L-aspartic or L-glutamic acid, which have 
excellent taste qualities associated with a very high sweetening potency 
of up to more than 20,000 times that of sucrose. 
A further object of the present invention is to provide a novel family of 
sweetening agents having a high stability compatible with the demands of 
industrial use. 
Thus, according to a first feature, the present invention relates to a 
novel sweetening agent of the following general formula: 
##STR13## 
in which: 
R is an acyl group of the formula 
##STR14## 
in which: 
R.sub.1 is a methyl, ethyl, propyl, isopropyl, phenyl, methoxy, ethoxy, 
trihalogenomethyl, chloro or chloromethyl radical; 
R.sub.2 is a hydrogen atom or a methyl, ethyl or methoxy radical; 
or R.sub.1 and R.sub.2, taken together with the carbon atom to which they 
are bonded, form a cycloalkyl group having from 3 to 6 carbon atoms; and 
R.sub.3 is an alkyl radical having from 3 to 11 carbon atoms, an alkenyl 
radical having from 3 to 7 carbon atoms, a cycloalkyl radical having from 
3 to 7 carbon atoms, a cycloalkylalkyl radical of which the cycloalkyl 
part has from 3 to 6 carbon atoms and the alkyl part has from 1 to 3 
carbon atoms, a phenyl radical, a phenylalkyl radical of which the alkyl 
part has from 1 to 3 carbon atoms, an alkoxy radical having from 3 to 10 
carbon atoms, a cycloalkoxy radical having from 3 to 6 carbon atoms, in 
which the two positions adjacent to carbon 1 attached to the oxygen can 
each be substituted by 1 or 2 methyl groups, a cycloalkylalkoxy radical of 
which the cycloalkyl part has from 3 to 6 carbon atoms and the alkoxy part 
has from 1 to 3 carbon atoms, a phenoxy radical or a phenylalkoxy radical 
of which the alkoxy part has from 1 to 3 carbon atoms; 
n is equal to 1 or 2; and 
R' is a group of the formula 
##STR15## 
in which Y and Z, which are identical or different, are N or CH, and in 
which X is selected from the group consisting of CN, NO.sub.2, Cl, 
CF.sub.3, COOCH.sub.3, COCH.sub.3, COCF.sub.3, CONH.sub.2, 
CON(CH.sub.3).sub.2, SO.sub.2 CH.sub.3, N.sub.3 and H; and to its 
physiologically acceptable salts. 
Within its framework, the invention comprises all the possible 
diastereoisomers of the compounds of formula (I) as well as mixtures 
thereof. 
In general formula (I), a trihalogenomethyl group is preferably a 
trifluoromethyl or trichloromethyl group. 
Furthermore, the alkyl, alkenyl or alkoxy groups can have a linear or 
branched chain. 
An alkyl radical having from 3 to 11 carbon atoms is for example a propyl, 
isopropyl, butyl, pentyl, isopentyl, hexyl, isohexyl, neohexyl, 
2,2-ditert-butylethyl or 3,3-ditert-butylpropyl group. 
An alkenyl radical having from 3 to 7 carbon atoms is for example a 
propenyl, butenyl, isopentenyl, isohexenyl or neoheptenyl group. 
An alkoxy radical having from 3 to 10 carbon atoms is for example a 
propoxy, isopropoxy, butoxy, pentoxy, hexyloxy, isohexyloxy, neoheptyloxy, 
ethylpropylmethoxy, dipropylmethoxy, ditert-butylmethoxy or 
ditert-butylethoxy group. 
A cycloalkoxy radical having from 3 to 6 carbon atoms, in which the two 
positions adjacent to carbon 1 attached to the oxygen can each be 
substituted by 1 or 2 methyl groups, is for example a cyclopropyl, 
cyclobutyl, 2,2,4,4-tetramethylcyclobutyl, cyclopentyl, 
2,2,5,5-tetramethylcyclopentyl, cyclohexyl, 2,6-dimethylcyclohexyl or 
2,2,6,6-tetramethylcyclohexyl group. 
In a preferred embodiment: 
R.sub.1 is a methyl, ethyl, phenyl, methoxy, ethoxy, trifluoromethyl, 
chloro or chloromethyl radical; 
R.sub.2 is a hydrogen atom or a methyl or ethyl radical; or R.sub.1 and 
R.sub.2, taken together with the carbon atom to which they are bonded, 
form a cyclopropyl, cyclobutyl or cyclopentyl group; and 
R.sub.3 is a normal alkyl radical having from 3 to 5 carbon atoms, a 
branched alkyl radical having from 3 to 7 carbon atoms, an alkenyl radical 
having from 3 to 7 carbon atoms, a cycloalkyl radical having from 3 to 6 
carbon atoms, a cycloalkylmethyl or cycloalkylethyl radical of which the 
cycloalkyl part has from 3 to 6 carbon atoms, a phenyl radical, a 
phenylmethyl radical, a phenylethyl or phenylisopropyl radical, an alkoxy 
radical having from 3 to 6 carbon atoms, a cycloalkoxy radical having from 
3 to 6 carbon atoms, a cycloalkylmethoxy radical of which the cycloalkyl 
part has from 3 to 6 carbon atoms, a phenoxy radical, or a phenylmethoxy 
or phenylethoxy radical; n and R' being as defined above. 
All the sweetening agents defined in this way have a high sweetening 
potency which is generally at least equal to that of the compounds of the 
state of the art having the most intense sweetening potencies. 
The invention is based on the totally unexpected discovery showing that the 
presence of a 2-substituted acyl group R in compounds derived from 
L-aspartic or L-glutamic acid results in a considerable increase in the 
sweetening potency of such compounds. 
Furthermore, it has been observed that the sweetening intensity of the 
compounds of the invention varies according to the configuration of the 
acyl group R (when R.sub.1, R.sub.2 and R.sub.3 are different radicals). 
For example, when R.sub.1 is a methyl group and R.sub.2 is a hydrogen atom, 
it is found, in the case where R.sub.3 is a butyl group, that the 
sweetening potency of the compounds in which the acyl group has an (S) 
configuration is higher than that of the corresponding compounds in which 
the acyl group has an (R) configuration. By contrast, when R.sub.3 is a 
phenoxy group, the sweetening potency of the compounds in which the acyl 
group has an (R) configuration is distinctly higher than that of the 
corresponding compounds in which the acyl group has an (S) configuration. 
It is for this reason that the compounds of formula (I) in which the acyl 
radical R has the following configuration: 
##STR16## 
in which R.sub.3 is as defined above, form a very advantageous class of 
compounds according to the invention. 
It has also been observed that, among these compounds, those derived from 
L-glutamic acid have a remarkable stability compatible with the most 
stringent industrial demands, especially those of the manufacture of soft 
drinks. 
Thus the derivatives of the invention of formula (I) in which n is equal to 
2 prove to be particularly advantageous and form a preferred subfamily of 
compounds of the invention. 
It has also been observed that the compounds of formula (I) in which the 
radical R' is a group of the formula 
##STR17## 
have a particularly high solubility and sweetening intensity because of 
the presence of the polar nitrogen atom in the ring, the compounds where X 
is CN being preferred. 
It is for this reason that another preferred class of compounds of the 
invention is represented by the following general formula: 
##STR18## 
in which R.sub.2 is a hydrogen atom or a methyl group and R.sub.3 is as 
defined above. 
The sweetening agents of this class have extremely high sweetening 
potencies, in particular when R.sub.3 is a butyl or phenoxy group. 
Thus the currently preferred compounds of the invention are as follows: 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile of 
the formula 
##STR19## 
N-(2,2-dimethylhexanoyl)-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile 
of the formula 
##STR20## 
N-[(R)-2-phenoxypropanoyl]-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile 
of the formula 
##STR21## 
In general, the compounds of the invention are distinguished from those 
described in the prior art by a distinctly higher sweetening potency, 
which can be up to more than 100 (one hundred) times greater. For example, 
some compounds of the invention have sweetening potencies which can be up 
to more than 20000 times that of sucrose; these are much more intense than 
the compounds of the prior art, whose sweetening potencies are very 
distinctly lower on average. 
As mentioned previously, compound (1) described in the documents U.S. Pat. 
Nos. 3,725,453 and 3,775,460 has a sweetening potency of 3000 times that 
of sucrose, compound (2) cited in the document JP-A-87-132847 has a 
sweetening potency of only 40 and compounds (3) and (4) described in the 
documents JP-A-87-252754 and EP-A-0.338.946 have respective sweetening 
potencies of 720 and 1000 times that of sucrose. 
Thus the compounds of the prior art which are the most advantageous from 
the point of view of their sweetening potency are 8 to 30 times less 
active than the preferred compounds of the invention. 
The stability of the compounds of the invention, in particular those 
containing the L-glutamyl residue, is very high and can in certain cases 
be about three hundred times greater than that of the compounds of the 
prior art. Thus, for example, an accelerated ageing study (prolonged 
heating at 70.degree. C. of an aqueous solution at pH 3) has been able to 
show that two compounds characteristic of the invention, namely compounds 
(5) and (6), have a half-life of about 60 (sixty) days under these 
accelerated ageing conditions. 
By way of comparison, the half-life of a few compounds described in the 
prior art was evaluated under these same standard conditions. Thus 
compound (1) described in the documents U.S. Pat. Nos. 3,725,453 and 
3,775,460 has a half-life of about 15 hours, compound (2) cited in the 
document JP-A-87-132847 has a half-life of about 20 hours, compound (3) 
described in the document JP-A-87-252754 has a half-life of about 8 hours 
and compound (4) described in the document EP-A-0.338.946 has a half-life 
of about 2 days. In all cases, the stability of the compounds 
characteristic of the present invention is much higher, the half-life 
being 30 to 300 times longer. 
Finally, compared with the synthetic sweetening agent most widely used at 
the present time, namely aspartame (7), whose sweetening potency is 180 
times that of sucrose, the preferred compounds of the invention are up to 
more than 120 times sweeter but also up to 60 times more stable, the 
half-life of aspartame being only 1 day under these standard conditions.

In conclusion, the presence of a 2-substituted acyl radical in the 
sweetening agents of the invention has the effect of spectacularly 
increasing the sweetening potency of the compounds derived from L-aspartic 
or L-glutamic acid, and hence of considerably reducing their cost price. 
This is coupled with an enhanced stability, in particular for the 
compounds of the invention which contain L-glutamic acid. To start with, 
it was not possible to speculate that the introduction of an acyl group 
substituted in the 2-position or that, for the preferred compounds of the 
invention, the choice of L-glutamic acid would lead to such a result, 
since, as is known, any modification, even slight, of the molecular 
structure of a sweetening agent can cause degradation both of the 
sweetening activity and of the related properties such as, for example, 
the stability. 
The sweetening agents of the present invention can be added to any edible 
product to which it is desired to give a sweet taste, provided that they 
are added in sufficient proportions to attain the desired level of 
sweetness. The optimal use concentration of the sweetening agent will 
depend on various factors such as, for example, the sweetening potency of 
the sweetening agent, the conditions of storage and use of the products, 
the particular constituents of the products, the taste profile of the 
edible products and the desired level of sweetness. Any qualified person 
can easily determine the optimal proportion of sweetening agent which must 
be employed to obtain an edible product, by performing routine sensory 
analyses. The sweetening agents of the present invention are generally 
added to the edible products in proportions ranging from 10 mg to 500 mg 
of sweetening agent per kilogram or per liter of edible product, depending 
on the sweetening potency of the compound. The concentrated products will 
obviously contain larger amounts of sweetening agent and will then be 
diluted in accordance with the intended final uses. 
The sweetening agents of the present invention can be added in the pure 
form to the products to be sweetened, but because of their high sweetening 
potency, they are generally mixed with an appropriate carrier or bulking 
agent. 
Advantageously, the appropriate carriers or bulking agents are selected 
from the group consisting of polydextrose, starch, maltodextrins, 
cellulose, methyl cellulose, carboxymethyl cellulose and other cellulose 
derivatives, sodium alginate, pectins, gums, lactose, maltose, glucose, 
leucine, glycerol, mannitol, sorbitol, sodium bicarbonate, phosphoric, 
citric, tartaric, fumaric, benzoic, sorbic and propionic acids and their 
sodium, potassium and calcium salts, and equivalents thereof. 
The present sweetening agents can be employed in an edible product by 
themselves, as the only sweetening agent, or in the form of mixtures of 
two or more sweetening agents of the present invention. In addition, the 
present sweetening agents can be used in combination with other sweetening 
agents such as sugars (sucrose), corn syrup, fructose, sweet dipeptide 
derivatives (aspartame, alitame), neohesperidin dihydrochalcone, 
hydrogenated isomaltulose, stevioside, the L sugars, glycyrrhizin, 
xylitol, sorbitol, mannitol, acesulfame-K, saccharin and its sodium, 
potassium, ammonium and calcium salts, cyclamic acid and its sodium, 
potassium and calcium salts, sucralose, monellin, thaumatin and 
equivalents thereof. 
In general, the compounds of the present invention can be prepared by any 
method which allows the formation of two amide bonds at the alpha-amino 
and alpha-carboxyl groups of L-aspartic acid (n=1) or L-glutamic acid 
(n=2). 
According to a second feature, the present invention relates to a method of 
preparing a sweetening agent of formula (I) as defined above, which 
comprises reacting the following with one another in any order: 
on the one hand L-aspartic acid or L-glutamic acid in which the beta- or 
gamma-carboxyl group, respectively, is protected if appropriate, and 
on the other hand: 
an acid of the formula 
##STR22## 
or its acid chloride; and an amine of the formula H.sub.2 N--R'; 
R.sub.1, R.sub.2, R.sub.3 and R' being as defined above; 
so as to create two amide bonds at the alpha-amino and alpha-carboxyl 
groups of the L-aspartic acid or L-glutamic acid; and 
if appropriate, converting the resulting product into a physiologically 
acceptable salt such as a sodium, potassium, ammonium, calcium or 
magnesium salt. 
This method therefore consists in forming an amide bond between an acid of 
the formula 
##STR23## 
or its acid chloride; 
and an amine of the formula 
##STR24## 
or in forming an amide bond between an acid of the formula 
##STR25## 
and an amine of the formula 
EQU H.sub.2 N--R' 
where R.sub.1, R.sub.2, R.sub.3, n and R' in these formulae are as defined 
above. 
These amide bonds can be produced by numerous methods described in the 
literature. The order in which each of these bonds is created depends on 
the choice made by those skilled in the art and on the particular 
techniques chosen. Thus the amide condensation reaction of a carboxylic 
acid with an amine can be performed either in the presence of a suitable 
dehydrating agent such as a carbodiimide, and especially with 
N,N'-dicyclohexylcarbodiimide, or by activating one of the two reactants, 
i.e. the amine or the carboxylic acid reactant. In this case, the carboxyl 
group can be activated by various methods, of which those involving the 
synthesis of a mixed anhydride, acid chloride, azide or activated ester 
intermediate (such as, for example, an ester of paranitrophenol or of 
N-hydroxysuccinimide) may be indicated in particular. 
In the particular case of L-aspartic or L-glutamic acid, it may sometimes 
prove necessary to protect the beta- or gamma-carboxyl group of the side 
chain before performing the amide condensation reaction. For this purpose, 
numerous protecting groups for the carboxyl group are described in the 
literature. Protection in the form of an ester is the most common, more 
particularly in the form of a tert-butyl ester or a benzyl ester. 
In certain cases, protection of this carboxyl group can nevertheless be 
avoided by forming an internal anhydride between on the one hand the 
alphacarboxyl group and on the other hand the beta- or gamma-carboxyl 
group of the L-aspartic or L-glutamic acid according to the equation 
##STR26## 
it being possible for the alpha-amino group to be either converted into a 
salt (for example the hydrochloride, sulfate or benzenesulfonate) or 
protected by a protecting group. For this purpose, numerous protecting 
groups for the alpha-amino group are described in the literature, such as, 
for example, trifluoroacetyl, benzyloxycarbonyl or tert-butoxycarbonyl. 
Another technique which makes it possible to avoid protection of this beta- 
or gamma-carboxyl group consists in performing the amide condensation 
reaction in aqueous solution, in which case activation is effected by 
converting the carboxylic acid (R.sub.1 R.sub.2 R.sub.3)CCOOH into the 
carboxylic acid chloride. It is then very advantageous to perform the 
reaction in a basic medium in a water/tetrahydrofuran mixture. The basic 
agent is preferably NaHCO.sub.3, Na.sub.2 CO.sub.3, NaOH or KOH. Examples 
which may be mentioned are the following reaction affording one of the 
precursors of the compounds of the invention: 
##STR27## 
or the following reaction affording the compounds of the invention direct: 
##STR28## 
The sweetening agents of the invention can also be converted into salts 
with physiologically acceptable inorganic or organic bases, which has the 
effect of considerably improving their rate of dissolution in aqueous 
solution. Advantageously, these compounds are converted into sodium, 
potassium, ammonium, calcium or magnesium salts. These salts can be 
prepared after concentration of an aqueous solution containing the 
compound of the invention and the chosen basic agent, such as, for 
example, NaOH or Na.sub.2 CO.sub.3 in the case of sodium salts. 
The purification of the compounds of the invention, in their acid or salt 
form, is carried out by the standard techniques such as recrystallization 
or chromatography. Their structure and their purity were checked by the 
conventional techniques (thin layer chromatography, high performance 
liquid chromatography (HPLC), infrared spectrometry, nuclear magnetic 
resonance, elemental analysis). 
The sweetening potency of the compounds described in the Examples was 
evaluated by a team of eight experienced people. This is done by comparing 
the taste of the compounds, in aqueous solution at variable 
concentrations, with a 2%, 5% or 10% reference solution of sucrose. The 
sweetening potency of the test compound compared with sucrose then 
corresponds to the weight ratio between the compound and sucrose for equal 
sweetening intensity, i.e. when the sweet tastes of the solution of the 
test compound and the reference solution of sucrose are considered, by a 
majority of people, to have the same sweetening intensity. 
The stability of the compounds of the prior art and those of the invention 
is measured using high performance liquid chromatography to determine the 
amount of product remaining after accelerated ageing in an acid medium 
(phosphate buffer at pH 3) and at high temperature (70.degree. C.). Under 
these experimental conditions, measurement of the half-life (time 
corresponding to 50% degradation) makes it possible to evaluate the 
potential stability of the compounds tested in this way. A compound of low 
stability will have a very short half-life of only a few hours, whereas a 
very stable compound will have a half-life of several tens of days, as is 
the case, for example, of compounds (5) and (6) of the invention, which 
have a half-life of about 60 days (FIG. 1). 
The way in which the invention can be carried out and the advantages 
resulting therefrom will become more apparent from the following 
non-limiting Examples. 
EXAMPLES 
Among the different possible preparative techniques for obtaining the 
compounds of the invention, one of the preferred techniques consists in 
condensing an amino derivative of the formula 
##STR29## 
with a carboxylic acid which has been activated beforehand in the form of 
the carboxylic acid chloride. The carboxylic acid is either commercially 
available or prepared by the methods described in the literature (for 
example J. Amer. Chem. Soc. 1970, 12, 1397). 
The amino derivative can advantageously be prepared by the procedure 
described in J. Med. Chem. 1973, 16, 163 from L-aspartic or L-glutamic 
acid and an amine H.sub.2 N--R', this latter amine generally being 
commercially available or prepared by the methods described in the 
literature (for example: Khim. Geterotsikl. Soedin., 1974, 12, 1645; Khim. 
Geterotsikl. Soedin., 1982, 11, 1545; Collect. Czech. Chem. Commun., 1975, 
40, 1384). 
1. Synthesis of 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile: 
##STR30## 
To prepare this compound, a solution of 1.2 g (0.008 mol) of 
(S)-2-methylhexanoyl chloride (prepared by reacting phosphorus 
pentachloride with (S)-2-methylhexanoic acid, itself obtained by the 
method described in J. Biol. Chem. 1926, 70, 211; ibid, 1932, 98, 1 and 
Chem. Pharm. Bull. 1979, 27, 747) in 30 cm.sup.3 of anhydrous 
tetrahydrofuran is added dropwise to a solution of 1 g (0.004 mol) of 
alpha-L-glutamyl-5-aminopyridine-2-carbonitrile (prepared according to J. 
Med. Chem. 1973, 16, 163) and 3.4 g (0.04 mol) of NaHCO.sub.3 in 30 
cm.sup.3 of water. After stirring for 15 minutes at 20.degree. C., the 
tetrahydrofuran is removed under vacuum and the remaining aqueous solution 
is acidified to pH 2-3 with a 6N solution of HCl, affording a precipitate 
of 1 g of 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile 
(yield 69%, melting point 146.degree. C., in the amorphous state) after 
filtration and trituration in hexane. 
The sweetening potency of this compound corresponds approximately, on a 
weight basis, to 20,000 (twenty thousand) times that of sucrose by 
comparison with a 2% solution of sucrose, 15,000 (fifteen thousand) by 
comparison with a 5% solution of sucrose, and 10,000 (ten thousand) by 
comparison with a 10% solution of sucrose; in other words, under these 
conditions, an aqueous solution of 10 mg/l of the compound has an intense 
sweet taste equivalent to that of a 10% solution of sucrose, which 
corresponds to the sweetening intensities generally used in food 
preparations. 
The stability of this compound is excellent. An evaluation performed by 
accelerated ageing under the standard conditions described above (pH 3, 
70.degree. C.) indicates that the half-life of the compound under these 
conditions is about 60 days. By virtue of its high sweetness and its high 
stability, it is therefore possible to envisage the widest use of this 
compound in food preparations. 
2. Synthesis of 
N-(2,2-dimethylhexanoyl)-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile: 
##STR31## 
This compound is obtained from 2,2-dimethylhexanoyl chloride (prepared by 
reacting phosphorus pentachloride with 2,2-dimethylhexanoic acid, obtained 
by the procedure described in J. Amer. Chem. Soc. 1970, 12, 1397) and 
alpha-L-glutamyl-5-aminopyridine-2-carbonitrile by the procedure described 
in the previous Example (yield 60%, melting point 138.degree. C., in the 
amorphous state). 
The sweetening potency of this compound corresponds approximately, on a 
weight basis, to 22,000 (twenty-two thousand) times that of sucrose by 
comparison with a 2% solution of sucrose, 15,000 (fifteen thousand) by 
comparison with a 5% solution of sucrose, and 14,000 (fourteen thousand) 
by comparison with a 10% solution of sucrose. 
The stability of this compound is also excellent, with a half-life 
evaluated under the standard conditions (pH 3, 70.degree. C.) at about 70 
days. As in the previous Example, it is therefore possible to envisage the 
use of this compound in food preparations. 
3. Synthesis of 
N-[(R)-2-phenoxypropanoyl]-alpha-L-glutamyl-5-aminopyridine-2-carbonitrile 
##STR32## 
This compound is obtained from (R)-2-phenoxypropanoyl chloride (obtained 
according to Nouv. J. Chim., 1982, 10, 685; Chem. Ber. 1984, 117, 3457; J. 
Chem. Soc. C. 1968, p. 1317; Ark. Kemi 1952, 4, 325) and 
alpha-L-glutamyl-5-aminopyridine-2-carbonitrile by the procedure described 
in the previous Example (yield 40%, melting point 110.degree. C., in the 
amorphous state). 
The sweetening potency of this compound corresponds approximately, on a 
weight basis, to 25,000 (twenty five thousand) times that of sucrose by 
comparison with a 2% solution of sucrose. Its stability, evaluated under 
the same standard experimental conditions (pH 3, 70.degree. C.), is also 
very high at about 60 days, which also makes it possible to envisage the 
very wide use of this compound in food preparations. 
4. Synthesis of 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-4-aminophenylcarbonitrile: 
##STR33## 
57.6 cm.sup.3 (0.408 mol) of trifluoroacetic acid anhydride is added 
dropwise to 30 g (0.408 mol) of L-glutamic acid. The mixture is heated for 
2 h at 70.degree. C. After removal of trifluoroacetic acid under vacuum, 
the oily residue thus obtained is triturated in an ethyl ether-hexane 
mixture. The N-trifluoroacetyl-L-glutamic acid anhydride obtained is 
directly used for the next step. 
A mixture of 30 g (0,133 mmol) of the anhydride thus obtained and 15.0 g 
(0,133 mol) of 4-aminobenzonitrile, in 100 cm.sup.3 of tetrahydrofuran, is 
stirred for 12 h at 40.degree. C. The tetrahydrofuran is removed under 
vacuum, and then the residue thus obtained is dissolved in 200 cm.sup.3 of 
a 5% solution of No.sub.2 CO.sub.3 and the resulting solution is washed 
with methylene chloride (3.times.100 cm.sup.3) and then acidified to pH 
2-3 with a 6N solution of HCl. The precipitate thus obtained is filtered, 
washed with some cm.sup.3 of water and dried, to give 27 g (yield 60%) of 
a mixture of alpha- and gamma-L-glutamyl-4-aminophenylcarbonitrile 
isomers. The alpha isomer is obtained separately after recrystallization 
in an ethanol-hexane mixture (150-90). 15 g of 
N-trifluoroacetyl-L-glutamyl-alpha-4-aminophenylcarbonitrile (final yield 
33%, melting point 197.degree. C.) is obtained. 
A solution of 2,5 g (7,28 mmol) of this compound in 25 cm.sup.3 of a 12.5% 
aqueous solution of ammoniac is stirred for 4 h at 20.degree. C. After 
concentration under vacuum, the resulting solid is washed with ethyl 
acetate (2.times.50 cm.sup.3) and then dried. 1,5 g of 
alpha-L-glutamyl-4-aminophenylcarbonitrile (yield 90%, melting point 
160.degree. C.) is obtained. 
To prepare 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-4-aminophenylcarbonitrile, 1,2 g 
(0,008 mol) of (S)-2-methylhexanoyl chloride (obtained by reaction of 
phosphorus pentachloride with the corresponding acid), in 30 cm.sup.3 of 
anhydrous tetrahydrofuran, is added dropwise to a solution of 1 g (0,004 
mol) of alpha-L-glutamyl-4-aminophenylcarbonitrile prepared according to 
the procedure described hereinabove and 3,3 g of NaHCO.sub.3 in 30 
cm.sup.3 of water. After stirring for 15 minutes at 20.degree. C., the 
tetrahydrofuran is removed under vacuum and the remaining aqueous solution 
is acidified to pH 2-3 with a 6N solution of HCl, affording a precipitate 
of 1 g of 
N-[(S)-2-methylhexanoyl]-alpha-L-glutamyl-4-aminophenylcarbonitrile (yield 
69%, melting point 143.degree. C., in the amorphous state) after 
filtration and trituration. 
The sweetening potency of this compound corresponds approximately, on a 
weight basis, to 9000 (nine thousand) times that of sucrose by comparison 
with 2% sucrose solution. The stability of this compound is excellent. Its 
half-life, evaluated under the conditions previously described (pH 3, 
70.degree. C.), is above 60 days. 
Summary Table 3 below gives, by way of examples, a list of a few compounds 
obtained by experimental protocols similar to those described above, which 
those skilled in the art will easily find, together with their relative 
sweetening potency (SP), evaluated on a weight basis, compared with a 2% 
aqueous solution of sucrose. When the groups R.sub.1, R.sub.2 and R.sub.3 
are different, the configuration of the asymmetric carbon to which they 
are bonded (carbon marked with an asterisk) is designated according to the 
conventional rules of stereochemistry using the R/S system: R, S or, when 
both configurations coexist in the same compound, RS. 
STABILITY STUDY 
FIG. 1 attached shows a comparative study of the degradation curves of a 
few compounds of the prior art, aspartame (the most widely used synthetic 
sweetening agent) and a few compounds of the invention, this study 
consisting of accelerated ageing of their solution in an acid medium (pH 
3) by heating at 70.degree. C. 
Curves (1) to (4) show the rapid degradation, under these conditions, of 
the compounds of formulae (1) to (4) described in the afore-mentioned 
prior art. The curve of compounds (5) and (6), on the other hand, is 
characteristic of the high stability of the compounds of the invention, in 
particular those containing L-glutamic acid. Finally, curve (7) shows the 
relatively low stability of aspartame, whose half-life under these same 
study conditions is only about 1 day. 
TABLE 3 
__________________________________________________________________________ 
##STR34## 
R.sub.1 
R.sub.2 
R.sub.3 * n Y Z X SP 
__________________________________________________________________________ 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.2 
R 2 CH CH CN 500 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.2 
S 2 CH CH CN 2800 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
R 2 CH CH CN 3000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
S 2 CH CH CN 9000 
CH.sub.3 
H (CH.sub.3).sub.2 CH(CH.sub.2).sub.2 
RS 
2 CH CH CN 6000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.4 
RS 
2 CH CH CN 1000 
CH.sub.3 
H C.sub. 6 H.sub.5 
R 2 CH CH CN 1300 
CH.sub.3 
H C.sub.6 H.sub.5 
S 2 CH CH CN 1500 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
R 2 N CH CN 2000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
S 2 N CH CN 20000 
CH.sub.3 
H C.sub.6 H.sub.5 
R 2 N CH CN 2500 
CH.sub.3 
H C.sub.6 H.sub.5 
S 2 N CH CN 4000 
CH.sub.3 
H c-C.sub.6 H.sub.11 
RS 
2 CH CH CN 1000 
C.sub.2 H.sub.5 
H CH.sub.3 (CH.sub.2).sub.3 
RS 
2 CH CH CN 5000 
C.sub.2 H.sub.5 
H C.sub.6 H.sub.5 
RS 
2 CH CH CN 2700 
C.sub.6 H.sub.5 
H C.sub.6 H.sub.5 
2 CH CH CN 250 
CH.sub.3 O 
H C.sub.6 H.sub.5 
RS 
2 CH CH CN 2300 
CH.sub.3 O 
H C.sub.6 H.sub.5 
R 2 N CH CN 11000 
CH.sub.3 O 
H C.sub.6 H.sub.5 
S 2 N CH CN 3000 
CH.sub.3 O 
H CH.sub.3 (CH.sub.2).sub.3 
RS 
2 N CH CN 2000 
CH.sub.3 
H C.sub. 6 H.sub.5 O 
RS 
2 CH CH CN 4000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.2 O 
R 2 CH CH CN 400 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.2 O 
S 2 CH CH CN 200 
CH.sub.3 
H (2,6-diMe)-c-C.sub.6 H.sub.9 O 
RS 
2 CH CH CN 1000 
CH.sub.3 
H C.sub.6 H.sub.5 O 
RS 
2 N CH CN 13000 
CH.sub.3 
H C.sub.6 H.sub.5 O 
R 2 N CH CN 25000 
Cl H C.sub.6 H.sub.5 
RS 
2 CH CH CN 2200 
CF.sub.3 
CH.sub.3 O 
C.sub.6 H.sub.5 
S 2 CH CH CN 600 
CH.sub.3 
CH.sub.3 
CH.sub.2 CHCH.sub.2 
2 CH CH CN 500 
CH.sub.3 
CH.sub.3 
CH.sub.3 (CH.sub.2).sub.3 
2 CH CH CN 11000 
CH.sub.3 
CH.sub.3 
(CH.sub.3).sub.2 CH(CH.sub.2).sub.2 
2 CH CH CN 10000 
CH.sub.3 
CH.sub.3 
(CH.sub.3).sub.3 CH(CH.sub.2).sub.2 
2 CH CH CN 4000 
CH.sub.3 
CH.sub.3 
CH.sub.3 (CH.sub.2).sub.3 
2 N CH CN 22000 
CH.sub.3 
CH.sub.3 
CH.sub.3 (CH.sub.2).sub.4 
2 N CH CN 3000 
CH.sub.2 CH.sub.2 
C.sub.6 H.sub.5 
2 CH CH CN 2500 
CH.sub.2 (CH.sub.2).sub.2 CH.sub.2 
C.sub.6 H.sub.5 
2 CH CH CN 2000 
CH.sub.2 (CH.sub.2).sub.2 CH.sub.2 
C.sub.6 H.sub.5 
2 N CH CN 3000 
CH.sub.2 CH.sub.2 
C.sub.6 H.sub.5 
1 CH CH CN 1000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
RS 
1 CH CH CN 1500 
CH.sub.3 
H C.sub.6 H.sub.5 O 
R 1 CH CH CN 18000 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
S 2 CH CH COCH.sub.3 
300 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
S 2 CH CH CONH.sub.2 
700 
CH.sub.3 
CH.sub.3 
CH.sub.3 (CH.sub.2).sub.3 
2 N CH Cl 600 
CH.sub.3 
H CH.sub.3 (CH.sub.2).sub.3 
S 2 N N CN 10000 
__________________________________________________________________________