Preparation of N-formamidinylamino acids from amino and formamidinesulfinic acids

Article abstract of DOI:10.1055/s-2000-8201

A practical synthetic procedure for the conversion of amino acids into N-formamidinylamino acids using formamidinesulfinic acid in basic water solution is presented.

Full text of DOI:10.1055/s-2000-8201

1656
SHORT PAPER
Preparation of N-Formamidinylamino Acids from Amino and
Formamidinesulfinic Acids
Branko S. Jursic,a* Donna Neumann,a Allen McPhersonb
aDepartment of Chemistry, University of New Orleans, New Orleans, Louisiana, 70148, USA
bStella Laboratories, L.L.C., 4801 Florida Ave. Suite #101, New Orleans, Louisiana 70117, USA
E-mail: bsjcm@uno.edu
Received 12 June 2000
with this reagent, we have decided to explore its N-form-
amidinylation capability with amino acids.
Abstract: A practical synthetic procedure for the conversion of
amino acids into N-formamidinylamino acids using formamidine-
sulfinic acid in basic water solution is presented.
To achieve our target, we have explored N-formamidin-
ylation reactions in aqueous ammonia. Both starting ma-
terials (glycine and formamidinesulfinic acid) are soluble
in aqueous ammonia, and after mixing these reagents,
white crystals were formed and a small amount of the
product (~10%) was obtained. In addition, very poor
yields of other products of amino acids were obtained in
ammonia. Not only was a small portion of the amino acid
transformed into the N-formamidinylamino acid, but also
separation of the product from the amino acid and the in-
organic salt formed in the course of the reaction is not an
easy task.
Key words: guanidino acids, guanylation, N-formamidinylamine
There is considerable interest for N-formamidinylamino
acid derivatives due to their exceptionally diverse biolog-
ical activity. Some areas of research concerned with the
biological activities of these compounds are in the fields
of the human cerebral arteries,1 neuronal nitric oxide syn-
theses,2,3 inhibition of spontaneous mammary tumors,4 re-
sistance of the influenza viruses,5 and anticancer
research.6 Common precursors for preparation of these
compounds are amino acids and cyanamide. This ap-
proach was originally introduced by Strecker7 and is prob-
ably the most versatile and most reliable procedure for the
preparation of non-substituted N-formamidinylamines in
general. Armstrong later improved this method.8 Weiss
and Krommer9 successfully used this approach for the
preparation of creatine on an industrial scale.10 For the
preparation other N-formamidine derivatives other than
creatine, this reaction is rather slow. To achieve a high
yield, stirring of the reaction mixture at room temperature
for several days is required. Other popular methods are re-
actions of amines with substituted S-methylisothiourea,11
or reactions of amines with 2,5-dimethyl-1-guanylpyra-
zole.12 The last two methods are generally better than the
cyanamide method, but the reactions usually require a
strong basic media and/or heat when carried out using
amino acids.13 There are several reports that use S-oxides
of thiourea for the preparation of N-formamidiny-
lamines.14,15 In their studies, Miller and Bischoff used for-
mamidesulfonic acid [HN=C(NH2)SO3H] and some N-
phenyl derivatives of this acid to prepare a few N-forma-
midinylamino acids in 25 85%.15 In theory, a more ac-
cessible formamidinesulfinic acid [HN=C(NH2)SO2H]
should also be useful as an N-formamidinylation reagent.
According to Miller and Bischoff, N-formamidinylation
of amino acids with this reagent is unreliable and the reac-
tion conversion is negligible.15 Actually, the first report of
N-formamidinesulfinic acid as an N-formamidinylation
reagent was reported by Walter.16 With this reagent,
N-formamidinylglycine was prepared from glycine in am-
monia in 34% yield.16 Considering the fact that valuable
N-formamidinyl amino acid derivatives can be prepared
If the same reaction is performed at room temperature
with an equivalent amount of aqueous sodium carbonate,
the reaction conversion is still very low. Changing the in-
troduction order of the reactants can substantially increase
the reaction conversion. Equivalent amounts of amino
acid and sodium carbonate were dissolved in water at an
elevated temperature and into this mixture (cooled to
room temperature) in small portions over a prolonged pe-
riod, the formamidine acid was added. The reaction mix-
ture was stirred at room temperature for several hours and
then at 60 °C for a half an hour. The N-formamidinylation
reaction was now performed with ~60% conversion, as
determined by comparison of the 1H NMR signals for hy-
drogen atoms attached to the chiral carbons of the amino
acid and the product.17 There are a few interesting obser-
vations that suggest that this method can be of preparative
use. First, the reaction should be performed in very con-
centrated water media. In many cases, during the course
of the reaction, a white precipitate is formed and if the re-
action mixture is too concentrated then its proper stirring
is hampered. Mechanical stirring of the reaction mixture
is advised instead of the more convenient magnetic stir-
ring. The best results are obtained when 0.1 mol of the
amino acid is dissolved in 30 mL of 0.1 mol aqueous so-
dium carbonate. Even in this case, the highest reaction
conversion was around 75%, with an isolation yield quite
lower than that due to difficulty in separating the product
from the starting amino acid and the inorganic salt.
One of the ways to eliminate the starting amino acid from
the reaction mixture is to assure its quantitative conver-
sion into the product. Therefore, we gradually increased
the amount of base and formamidinesulfinic acid. Indeed,
Synthesis 2000, No. 12, 1656–1658 ISSN 0039-7881 © Thieme Stuttgart · New York

SHORT PAPER
Preparation of N-Formamidinylamino Acids from Amino and Formamidinesulfinic Acids
1657
1H NMR signals for the starting amino acid were not product, cyanoguanidine can be removed by washing the
present or were substantially diminished, but with the crystalline product with methanol (Procedure A).
40% excess of formamidinesulfinic acid, a new byprod-
If the product of the reaction is substantially soluble in
uct, cyanoguanidine [HN=C(NH2)NHCN], was formed.18
water, then the isolation method presented in procedure A
Although cyanoguanidine can be eliminated from the
is not appropriate. In these cases, a dry work-up of the re-
product by several crystallizations, the isolated yield after
action mixture was necessary (Procedure B). After the re-
action was completed, the water was evaporated at almost
several crystallizations is still around 30 40%.
In further optimization of the reaction conditions, the room temperature and a white solid was extracted with hot
base, sodium carbonate, was replaced with sodium hy- methanol. With this approach, the yield of N-formamidi-
droxide (2.3 equivalents) and the formamidinesulfinic nylamino acid is considerably higher. The yields of prod-
acid molar ratio was increased to 1.13 equivalents in re- ucts generated with these two methods are listed in Table.
gards to the amino acid. The amino acid/water ratio was Unfortunately, this method is not applicable to low-basic
also increased to a 0.1 mol/40 mL ratio to insure better anilines such as 4-aminobenzoic acid. In this particular
stirring of the highly viscous reaction suspension. Under case, only 5 10% reaction conversion was observed.
these reaction conditions, almost quantitative amino acid Therefore, we believe that this approach should not be
1
conversion into product was observed in the crude H practical for slightly nucleophilic amines, such as aniline
NMR spectra. Furthermore, a minimal amount of the cy- derivatives but it should be the method of choice for con-
anoguanidine was formed.
version of aliphatic amines into the corresponding N-for-
mamidinyl derivatives.
As in previous cases, separation of the product from small
quantities of starting amino acid and cyanoguanidine, as
well as the formed inorganic salt was not an easy task.
Most of N-formamidinylamino acids are soluble in water,
Mps were determined on an Electrothermal IA 9000 Digital Melting
Point Apparatus. Mass Spectroscopy was performed on a Micro-
therefore their separation from the inorganic salt by crys- mass Quattro 2 Triple Quadrapole Mess Spectrometer. The 1H and
13C NMR spectra were recorded on a Varian Gemini NMR spec-
tallization is an almost impossible task. On the other hand,
amino acids with sizeable organic parts such as phenyla-
trometer (400 MHz) with D2O or D2O/DMSO-d6 as solvent.
lanine, phenylglycine, and 5-aminopentanoic acid pro-
duce a less water soluble product and can be separated
from salt by crystallization from water. It is important to
perform the first crystallization with a minimal amount of
water. After the first crystallization, the solubility of the
product in water is substantially diminished. The other by-
D,L-N-Formamidinephenylalanine; Typical Procedure A
Into aqueous NaOH (40 mL, 9.2 g, 0.23 mol) and D,L-phenylala-
nine (16.5 g, 0.1 mol), formamidinesulfinic acid (12.4 g, 0.115 mol)
was added in small portions over 30 min. After approx. 1/3 of for-
mamidinesulfinic acid was added, the reaction mixture became a
viscous suspension. The suspension was stirred at r.t. overnight and
then heated to 60 C and stirred for an additional 30 min. The crys-
Table Yields of N-Foramidine Amino Acids 2
Entry
Method
Amino Acid 1
N-Formamidine 2a
Yield (%)b
2
2
3
4
5
6
7
8
9
B
A
B
B
B
A
B
A
A
B
A
B
Glycine
N-Formamidineglycine
70.2
70.2
83.2
73.2
72.1
78.2
91.8
78.2
82.4
32.0
63.2
39.3
Glycylglycine
N-Methylglycine
L-Alanine
N-Formamidineglycylglicine
N-Formamidine-N-methylglycine
N-Formamidine-L-alanine
-Alanine
N-Formamidine- -alanine
4-Aminopentane
L-Tryptophan
D,L-Phenylalanine
L-Phenylglycine
L-Valine
N-Formamidine- -alanine-4-aminopentane
N-Formamidine- -L-tryptophan
N-Formamidine-D,L-phenylalanine
N-Formamidine-L-phenylglycine
N-Formamidine-L-valine
10
11
12
L-Leucine
L-Methionine
N-Formamidine-L-leucine
N-Formamidine-L-methionine
aAll products were characterized by comparison of their mps, IR and 1H NMR spectra from references 10 and 16.
bIsolated yields.
Synthesis 2000, No. 12, 1656–1658 ISSN 0039-7881 © Thieme Stuttgart · New York

1658
B. S. Jursic et al.
SHORT PAPER
talline product was separated by cold filtration. White solid was
crystallized from H2O, and the resulting white crystals were washed
with small portions of cold MeOH.
MS (electrospray, ES+, CH3OH/H2O): m/z = 129.9, 147.8, 178.8,
211.7, 214.8, 229.7, 230.8, 247.7, 251.6, 269.5 (M+Na)+, 270.5,
271.5
Yield: 16.2 g (78.2%), mp: ~235 °C (dec.).
1H NMR (400 MHz, D2O): = 7.28 (dt, 2H, J = 0.018, 0.003 Hz),
7.27 (dt, 1H, J = 0.018, 0.08 Hz), 7.18 (dd, 2H, J = 0.019, 0.008
Hz), 4.10 (dd, 1H, J = 0.019, 0.011 Hz), 3.15 (dd, 1H, J = 0.035,
0.011 Hz), 2.90 (dd, 1H, J = 0.035, 0.020 Hz).
13C (100MHz, D2O/DMSO-d6/NaOH): = 180, 160, 139, 130,
129,128, 59, 39.
References
(1) Segarra, G.; Medina, P.; Lluch, S. Stroke 1999, 30, 2206.
(2) Tierney, D. L.; Martasek, P.; Hoffman, B. M. J. Am. Chem.
Soc. 1998, 120, 2983.
(3) Morita, H.; Yoshikawa, H.; Tanaka, H. J. Bacteriol. 1997,
179, 7812.
MS (electrospray, ES+, CH3OH/H2O): m/z = 188.7, 208.6, 213.6,
(4) Tsunoda, S.; Kawamoto, H. Nagasawa, H, Anticancer Res.
1997, 17, 347.
230.6 (M+Na)+, 231.7, 232.5.
(5) Staschke, K. A.; Colacino, J. M.; Lawer, W. G. Virology 1995,
214, 642.
(6) Katsura, Y.; Inoue, Y.; Tomishi, T. J. Med. Chem. 1994, 37,
57.
L-N-Formamidinetryptophan; Typical Procedure B
NaOH (9.2 g, 0.23 mol) was dissolved in H2O (40 mL) and L-tryp-
tophan (20.4 g, 0.1 mol) was added. Into the clear reaction mixture
at r.t. and with vigorous stirring, small portions (1 g/3 min) of for-
mamidinesulfinic acid (12.4 g, 0.115 mol) was added. After all for-
mamidinesulfinic acid was added, a very hard to stir reaction
suspension was agitated at r.t. overnight. Into the suspension, EtOH
(100 mL) and toluene (300 mL) were added and these solvents were
evaporated at ~30 °C under reduced pressure. The same procedure
was repeated two more times to eliminate traces of H2O. The solid
residue was slurred into MeOH (1 L) and refluxed for several hours.
The liquid was separated from the solid inorganic material by hot
filtration and concentrated into a smaller volume (100 mL). The
product was crystallized from MeOH by standing at r.t. for several
days. Resulting white crystals were separated by filtration.
(7) Strecker, C. R. Acad. Sci., Paris 1861, 52, 1212.
(8) Armstrong, M. D. J. Org. Chem. 1956, 21, 503.
(9) Weiss, S.; Krommer, H. U.S. Patent No. 1998, 5719319.
(10) Rowley, G. L.; Greenleaf, A. L.; Kenyon, G. L. J. Am. Chem.
Soc. 1971, 93, 5542.
(11) Lai, B.; Gangopadhyay, Tetrahedron Lett. 1996, 37, 2483.
(12) Short, J. H.; Biermacher, U.; Dunningan, D. A. Leth, T. D. J.
Med. Chem. 1963, 6, 275; and references therein.
(13) Pant, R. Z. Physiol. Chem. 1964, 334, 272.
(14) Durant, G. J.; Young, R. C.; Tashman, Z. U. S. Patent
4,210,658, 1980.
(15) Miller, C. E.; Bischoff, J. J. Synthesis 1986, 777.
(16) Walter, W. Angew. Chem. 1955, 67, 275.
(17) For the N-formadinylamino acid, the 1H NMR chemical shift
for hydrogen attached to chiral carbon is 0.2 ppm higher than
that of the amino acid.
(18) Byproduct, HN=C(NH2)NHCN is probably formed by
cyanamide dimerization after the (Na2SO2) is eliminated in
sodium hydroxide water solution of formamidinesulfinic acid.
Yield: 22.6 g (91.8%), mp: ~225 °C (dec.).
1H NMR (400 MHz, D2O): = 10.84 (s, 1H), 7.49 (d, 1H, J = 0.021
Hz), 7.32 (br s, 1H), 7.29 (d, 1H, J = 0.021 Hz), 7.06 (d, 1H,
J = 0.005 Hz), 7.01 (dt, 1H, J = 0.017, 0.003 Hz), 6.92 (dt, 1H,
J = 0.019, 0.002 Hz), 4.05 (dd, 1H, J = 0.037, 0.019 Hz), 3.21 (dd,
1H, J = 0.026, 0.011 Hz).
13C NMR (100 MHz, D2O/DMSO-d6/NaOH): = 178, 159, 137,
128, 124, 122, 120, 119, 112.7, 112, 58, 29.
Article Identifier:
1437-210X,E;2000,0,12,1656,1658,ftx,en;M00500SS.pdf
Synthesis 2000, No. 12, 1656–1658 ISSN 0039-7881 © Thieme Stuttgart · New York