Method of preparing salicyloylamino acids

A method for preparing salicyloylamino acids is provided. An oligosalicylate and an amino acid are reacted to yield the salicyloylamino acid.

FIELD OF THE INVENTION 
The present invention relates to methods for preparing salicyloylamino 
acids. Certain salicyloylamino acids are useful in the delivery of active 
agents, such as for example, biologically or chemically active agents, to 
a target. 
BACKGROUND OF THE INVENTION 
Certain salicyloylamino acids have been demonstrated as being useful in the 
delivery of active agents, particularly, through the oral route. See, for 
example, U.S. patent application Ser. No. 08/414,654, now U.S. Pat. No. 
5,650,386, filed Mar. 31, 1995, now U.S. Pat. No. 5,650,386. 
Two methods of preparation of such compounds are illustrated in U.S. patent 
application Ser. No. 08/414,654, now U.S. Pat. No. 5,650,386, filed Mar. 
31, 1995 and provisional U.S. patent application Ser. No. 60/003,111, 
filed Sep. 1, 1995, published as WO96/30036, Oct. 3, 1996. 
Additionally, Ho et al., Synthetic Communications, 26(14), 2641-2649 (1986) 
summarizes a number of methods for the preparation of 
.omega.-aminoalkanoic acids. These methods include the introduction of an 
amine group by the conversion of a ketone to an oxime or a carboxylate to 
a nitrile, followed by reduction by azidide opening of an anhydride, 
followed by Schmidt rearrangement, or by Hoffman rearrangement of an amide 
with aqueous base and bromine. Boc protected and N-acylated .omega.-amino 
alkanoic acids can also be obtained by hydrolysis of the N-Boc and 
N-acylated lactams, respectively. Ho et al. presents an additional 
synthetic route to N-Boc protected or Boc-amino acid coupled with 
.omega.-aminoalkanoic acids. 
However, there is still a need for an efficient, economical, and 
commercially practical method for the preparation of salicyloylamino 
acids. 
SUMMARY OF THE INVENTION 
A method for preparing a salicyloyl amino acid is provided in which an 
oligosalicylate and an amino acid are reacted to yield the salicyloyl 
amino acid. 
DETAILED DESCRIPTION OF THE INVENTION 
Oligosalicylates are typically represented by the formula 
##STR1## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently hydrogen, 
fluorine, chlorine, bromine, iodine, C.sub.1-9 linear or branched chain 
alkyl, C.sub.1-9 linear or branched chain alkoxy, C.sub.6-14 aryl, 
C.sub.6-14 aryloxy or (C.sub.6-14 aryl)(C.sub.1-9 linear or branched chain 
alkyl); and wherein n is an integer from about 1 to about 10. 
Preferred oligosalicylates are represented by the formulae 
##STR2## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently hydrogen, 
fluorine, chlorine, bromine, iodine, C.sub.1-9 linear or branched chain 
alkyl, C.sub.1-9 linear or branched chain alkoxy, C.sub.6-14 aryl, 
C.sub.6-14 aryloxy or (C.sub.6-14 aryl)(C.sub.1-9 linear or branched chain 
alkyl); and wherein n is an integer from about 1 to about 10; 
##STR3## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently hydrogen, 
fluorine, chlorine, bromine, iodine, C.sub.1-9 linear or branched chain 
alkyl, C.sub.1-9 linear or branched chain alkoxy, C.sub.6-14 aryl, 
C.sub.6-14 aryloxy or (C.sub.6-14 aryl)(C.sub.1-9 linear or branched chain 
alkyl); and wherein n is an integer from about 1 to about 10; and 
##STR4## 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently hydrogen, 
fluorine, chlorine, bromine, iodine, C.sub.1-9 linear or branched chain 
alkyl, C.sub.1-9 linear or branched chain alkoxy, C.sub.6-14 aryl, 
C.sub.6-14 aryloxy or (C.sub.6-14 aryl)(C.sub.1-9 linear or branched chain 
alkyl); and wherein n is an integer from about 1 to about 10. 
Most preferred oligosalicylates are oligosalicylate, oligo-methyl 
salicylate, and oligo-dichlorosalicylate. 
An amino acid is any carboxylic acid having at least one free amine group 
and includes naturally occurring and synthetic amino acids. Many amino 
acids and amino acid esters are readily available from a number of 
commercial sources such as Aldrich Chemical Co. (Milwaukee, Wis., USA); 
Sigma Chemical Co. (St. Louis, Mo., USA); and Fluka Chemical Corp. 
(Ronkonkoma, N.Y. USA). 
Representative, but not limiting, amino acids for use in the present 
invention are generally of the formula 
##STR5## 
wherein: R.sup.5 is hydrogen, C.sub.1 -C.sub.4 alkyl, or C.sub.2 -C.sub.4 
alkenyl; 
R.sup.6 is C.sub.1 -C.sub.24 alkyl, C.sub.2 -C.sub.24 alkenyl, C.sub.3 
-C.sub.10 cycloalkyl, phenyl, naphthyl, (C.sub.1 -C.sub.10 alkyl) phenyl, 
(C.sub.2 -C.sub.10 alkenyl) phenyl (C.sub.1 -C.sub.10 alkyl) naphthyl, 
(C.sub.2 -C.sub.10 alkenyl) naphthyl, phenyl (C.sub.1 -C.sub.10 alkyl), 
phenyl (C.sub.2 -C.sub.10 alkenyl), naphthyl (C.sub.1 -C.sub.10 alkyl), or 
naphthyl (C.sub.2 -C.sub.10 alkyl) or naphthyl (C.sub.2 -C.sub.10 
alkenyl); 
R.sup.6 being optionally substituted with C.sub.1 -C.sub.4 alkyl, C.sub.2 
-C.sub.4 alkyenyl, C.sub.1 -C.sub.4 alkoxy, --OH, --SH, --CO.sub.2 
R.sup.7, C.sub.3 -C.sub.10 cycloalkyl, C.sub.3 -C.sub.10 cycloalkenyl, 
heterocycle having 3-10 ring atoms wherein the hetero atom is one or more 
of N, O, S, or any combination thereof, aryl, (C.sub.1 -C.sub.10 alk)aryl, 
ar(C.sub.1 -C.sub.10 alkyl) or any combination thereof; 
R.sup.6 being optionally interrupted by oxygen, nitrogen, sulfur, or any 
combination thereof; and 
R.sup.7 is hydrogen, C.sub.1 -C.sub.4 alkyl, or C.sub.2 -C.sub.4 alkenyl. 
The preferred naturally occurring amino acids are alanine, arginine, 
asparagine, aspartic acid, citrulline, cysteine, cystine, glutamine, 
glycine, histidine, isoleucine, leucine, lysine, methionine, ornithine, 
phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, 
hydroxy proline, .gamma.-carboxyglutamate, phenylglycine, or 
O-phosphoserine. The preferred amino acids are arginine, leucine, lysine, 
phenylanine, tyrosine, tryptophan, valine, and phenylglycine. 
The preferred non-naturally occurring amino acids are .beta.-alanine, 
.alpha.-amino butyric acid, .gamma.-amino butyric acid, 
.gamma.-(aminophenyl) butyric acid, .alpha.-amino isobutyric acid, 
citrulline, .epsilon.-amino caproic acid, 7-amino heptanoic acid, 
.beta.-aspartic acid, aminobenzoic acid, aminocaprylic acid, aminophenyl 
acetic acid, aminophenyl butyric acid, .gamma.-glutamic acid, cysteine 
(ACM), .epsilon.-lysine, .epsilon.-lysine (A-Fmoc), methionine sulfone, 
norleucine, norvaline, ornithine, d-ornithine, p-nitro-phenylalanine, 
hydroxy proline, 1,2,3,4,-tetrahydroisoquinoline-3-carboxylic acid, 
aminodecanoic acid, and thioproline. Most preferred amino acids are 
aminocaprylic acid and aminodecanoic acid. 
Poly amino acids are either peptides or two or more amino acids linked by a 
bond formed by other groups which can be linked, e.g., an ester, anhydride 
or an anhydride linkage. Poly amino acids can be homo- or hetero-poly 
amino acids, and can include natural amino acids, synthetic amino acids, 
or any combination thereof. 
Peptides are two or more amino acids joined by a peptide bond. Peptides can 
vary in length from di-peptides with two amino acids to polypeptides with 
several hundred amino acids. See, Walker, Chambers Biological Dictionary, 
Cambridge, England: Chambers Cambridge, 1989, page 215. 
The present reaction is typically conducted in an aqueous medium (which can 
contain sodium hydroxide) and in the presence of one or more organic 
solvents such as, for example, dioxane, xylenes, acetonitrile, 
tetrahydrofuran, and 1-methoxy-2-propanol. Preferred reaction temperatures 
range from about 25 degrees C. to about 150 degrees C. Preferred reaction 
times range from about 0.5 to about 24 hours. Typically, the molar ratio 
of the oligosalicylate reactant to the amino acid reactant will range from 
about 0.5 to about 2.0. 
The reaction product can be isolated from the reaction mixture by, for 
example, filtration followed by drying of the filtrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following Examples illustrate the invention without limitation. All 
parts are given by weight unless otherwise indicated. 
EXAMPLE 1 
Preparation of N-(salicyloyl)-8-aminocaprylic acid 
A. Preparation of Cyclooctanone Oxime Hydrochloride 
##STR6## 
Cyclooctanone (50 g, 0.396 mol, 1.0 eq) and ethanol (250 mL) were placed in 
a 500 mL round bottom flask equipped with a magnetic stir bar. 
Hydroxylamine hydrochloride (28.91 g, 0.416 mol, 1.05 eq) was added 
slowly. The cloudy reaction mixture was stirred at 25 degrees C. for 20 
min and heated to 50 degrees C. for 30 min, during which time it turned 
clear. Upon cooling to 25 degrees C., the mixture was concentrated to 
produce an off-white solid, which still contained a small amount of 
ethanol. The cyclooctanone oxime hydrochloride was used without further 
purification. 
B. Preparation of 2-Azacyclononanone 
##STR7## 
Cyclooctanone oxime hydrochloride (6.7 g., 39.6 mmol, 1.0 eq) and formic 
acid (15 mL) were placed in a 100 mL round bottom flask equipped with a 
magnetic stirrer, a cold-water condenser and a nitrogen purge. The mixture 
was treated with concentrated sulfuric acid (2.1 mL, 39.6 mmol, 1.0 eq) 
and heated to reflux. After 3.5 hours, no starting material was observed 
by TLC. The now black reaction mixture was cooled to 25 degrees C. and 
poured slowly into 200 mL of ice water. The pH was adjusted to 7.5-8.0 
with 10N NaOH. The aqueous mixture was extracted with chloroform (3 
times). 
The combined organic layers were dried over Na.sub.2 SO.sub.4 and 
concentrated in vacuo. The residue was purified by Kugelrohr distillation. 
The 2-azacyclononanone was isolated as a colorless liquid (3.76 g, 75%). 
C. Preparation of 2-Azacyclononanone 
Polyphosphoric acid (31.9 g) and water (3.75 g) were placed in a 100 mL 
round bottom flask equipped with a stir bar and a cold water condenser. 
The mixture was heated to 130 degrees C., and cyclooctanone oxime 
hydrochloride (5.9 g, 35 mmol, 1.0 eq) was added in small portions over 10 
min. The oxime dissolved readily. The reaction mixture was stirred at 130 
degrees C. for 1 hour, turned dark, was cooled to 100 degrees C., and 
poured into 100 mL of ice water. The aqueous mixture was extracted with 
chloroform (3.times.75 mL). The combined organic layers were dried over 
Na.sub.2 SO.sub.4 and concentrated in vacuo. The 2-azacyclononanone slowly 
crystallized into an off-white solid (4.69 g, 94%). 
D. Preparation of Oligosalicylate 
##STR8## 
Acetic anhydride (14.50 mL, 15.69 g, 0.154 mol, 1.02 eq), salicylic acid 
(20.79 g, 0.151 mmol, 1.00 eq), and xylenes (60 mL) were added to a 250 
mL, three-neck flask fitted with a magnetic stir bar, a thermometer, and a 
DeanStark trap with condenser. The flask was placed in a sand bath and 
heating of the cloudy white mixture was begun. The reaction mixture became 
a clear solution around 100 degrees C. Most of the volatile organics 
(xylenes and acetic acid) distilled into the Dean-Stark trap over three 
hours (135-146 degrees C). Distillation was continued for another hour (a 
total of 75 mL distilled), during which the pot temperature slowly rose to 
195 degrees C. and the distillate slowed to a trickle. The residue was 
poured off while still hot into an aluminum tray. Upon cooling a brittle 
yellow glass formed. The solid was ground to a fine powder. The 18.95 g of 
oligosalicylate produced was used without further purification. 
E. Preparation of Salicyloylamino acid 
##STR9## 
A 10N sodium hydroxide solution of (4.4 mL, 44.0 mmol, 1.18 eq), 
8-aminocaprylic acid (5.93 g, 37.2 mmol, 1.00 eq), sodium bicarbonate 
(0.88 g, 10.4 mmol, 0.28 eq) and water (5 mL) were added to a 250 mL round 
bottom flask equipped with a magnetic stir bar and an addition funnel. The 
white cloudy mixture was treated with a solution of oligosalicylate (5.20 
g, 42.9 mmol 1.15 eq) and dioxane (20 mL), added over five minutes. The 
addition funnel was replaced with a condenser, and the reaction mixture 
was heated to 90 degrees C. for 3 hours (at which time the reaction was 
determined to have finished, by HPLC). The clear orange reaction mixture 
was cooled to 40 degrees C., filtered and acidified to pH=1 with 3% (by 
vol.) aqueous hydrochloric acid. All of the dioxane and some of the water 
were stripped (60 degrees C., 50 mm). The solid (which precipitated from 
solution during stripping) was isolated by filtration while still warm. 
The light pink solid was recrystallized from 50 mL of 65% ethanol-water. 
The solid was recovered by filtration and was dried over 18 hours in a 50 
degrees C. vacuum oven. The N-(salicyloyl)-8-aminocaprylic acid was 
isolated as a white solid (5.35 g, 51%). 
F. Preparation of Salicyloylamino acid 
##STR10## 
Sodium hydroxide (1.68 g, 42.0 mmol, 1.2 eq), 2-azacyclononanone (5.0 g, 
35.5 mmol, 1.0 eq) and 20 mL of water were placed a 100 mL round bottom 
flask equipped with a magnetic stir bar and cold water condenser to 
prepare aminocaprylic acid. The reaction mixture was heated to reflux for 
2.5 hours (at which time the reaction was determined to have finished, by 
TLC) and cooled to 25 degrees C. A solution of oligosalicylate (4.87 g, 40 
mmol, 1.1 eq) and dioxane (50 mL) was added to the aqueous solution of 
8-aminocaprylic acid. This mixture was heated to reflux for 2.25 hours (at 
which time the reaction was determined to have finished, by HPLC). The 
clear orange reaction mixture was cooled to 25 degrees C. and acidified to 
pH=1 with 3% (by vol.) aqueous hydrochloric acid. All the dioxane and some 
of the water were stripped (60 degrees C., 50 min). The aqueous phase was 
decanted from the brown oil while still warm. Crystallization of the oil 
from ethanol-water yielded a white precipitate. The solid was recovered by 
filtration and was dried over 4 hours in a 50 degrees C. vacuum oven. The 
N-(salicyloyl)-8-aminocaprylic acid was isolated as a white solid (5.73 g, 
59%). 
EXAMPLE 2 
Preparation of Oligo(3-methylsalicylate) 
A. Preparation of Oligo N-(3-methylsalicyloyl)-8-aminocaprylic Acid 
##STR11## 
Acetic anhydride (11.10 mL, 12.01 g, 0.118 mol, 1.03 eq), 3-methylsalicylic 
acid (17.37 g, 0.114 mmol, 1.00 eq), and xylenes (60 mL) were added to a 
250 mL, three-neck flask fitted with a magnetic stir bar, a thermometer, 
and a Dean-Stark trap with condenser. The flask was placed in a sand bath 
and heating of the cloudy white mixture was begun. The reaction mixture 
cleared to a yellow solution around 100 degrees C. Most of the volatile 
organics (xylenes and acetic acid) were distilled into the Dean-Stark trap 
over three hours (135-146 degrees C.). Distillation was continued for 
another hour (a total of 75 mL distilled), during which the pot 
temperature slowly rose to 175 degrees C. and the distillate slowed to a 
trickle. The residue was poured off while still hot into an aluminum tray. 
Upon cooling a brittle yellow glass formed. The solid was ground to a fine 
powder. The 15.90 g of oligo(3-methylsalicylate) produced was used without 
further purification. 
B. Preparation of Salicyloylamino acid 
##STR12## 
A 50% (by weight) solution of potassium carbonate (24 mL, 36 g, 0.127 mol, 
1.23 eq), 8-aminocaprylic acid (16.44 g, 0.103 mol, 1.00 eq), and water 
(20 mL) were added to a 250 mL round bottom flask equipped with a magnetic 
stir bar and an addition funnel. The white cloudy mixture was treated with 
a solution of oligo(3-methylsalicylate) (15.90 g, 0.114 mmol 1.11 eq) and 
dioxane (90 mL), added over five minutes. The addition funnel was replaced 
with a condenser, and the reaction mixture was heated to 90 degrees C. for 
4 hours (at which time the reaction was determined to have finished, by 
HPLC). The clear orange reaction mixture was cooled to 40 degrees C. and 
acidified to pH=1 with 3% (by vol.) aqueous hydrochloric acid. All the 
dioxane and some of the water were stripped (60 degrees C., 50 mm). The 
water layer from the resulting two-phase mixture was decanted while still 
warm. The orange oil was crystallized from 65% ethanol-water to give a tan 
solid upon cooling to -10 degrees C. The solid was recrystallized from 50 
mL of 65% ethanol-water. The off-white solid was washed with hot water (30 
mL) to remove most of the remaining salicylic acid. The solid was 
recovered by filtration and was dried over 6 hours in a 50 degrees C. 
vacuum oven. The N-(3-methylsalicyloyl)-8-aminocaprylic acid was isolated 
as a light tan solid (12.32 g, 41%). 
EXAMPLE 3 
Preparation of N-(4-methylsalicyloyl)-8-aminocaprylic acid 
A. Preparation of Oligo(4-methylsalicylate) 
##STR13## 
Acetic anhydride (14.60 mL, 15.80 g, 0.155 mol, 1.04 eq), 4-methylsalicylic 
acid (22.68 g, 0.149 mmol, 1.00 eq) and xylenes (90 mL) were added to a 
250 mL, three-neck flask fitted with a magnetic stir bar, a thermometer, 
and a Dean-Stark trap with condenser. The flask was placed in a sand bath 
and heating of the cloudy white mixture was begun. The reaction mixture 
cleared to a yellow solution around 90.degree. C. Most of the volatile 
organics (xylenes and acetic acid) were distilled into the Dean-Stark trap 
over three hours (135-146 degrees C.). Distillation was continued for 
another hour (a total of 110 mL distilled), during which the pot 
temperature slowly rose to 183 degrees C. and the distillate slowed to a 
trickle. The residue was poured off while still hot into an aluminum tray. 
Upon cooling a brittle yellow glass formed. The solid was ground to a fine 
powder. The 20.65 g of oligo(4-methylsalicylate) received was used without 
further purification. 
B. Preparation of Salicyloylamino acid 
##STR14## 
A 50% (by weight) solution of potassium carbonate (30 mL, 44.6 g, 0.161 
mol, 1.19 eq), 8-aminocaprylic acid (21.43 g, 0.135 mol, 1.00 eq), and 
water (20 mL) were added to a 250 mL round bottom flask equipped with a 
magnetic stir bar and an addition funnel. The white cloudy mixture was 
treated with a solution of oligo(4-methylsalicylate) (20.65 g, 0.152 mmol 
1.13 eq) and dioxane (80 mL), added over five minutes. The addition funnel 
was replaced with a condenser, and the reaction mixture was heated to 90 
degrees C. for 4 hours (at which time the reaction was determined to have 
finished, by HPLC). The clear orange reaction mixture was cooled to 30 
degrees C. and acidified to pH=1 with 3% (by vol) aqueous hydrochloric 
acid. All of the dioxane and some of the water were stripped (600 C, 50 
mm). The solid (which precipitated from solution during stripping) was 
isolated by filtration while still warm. The light pink solid was 
recrystallized from 80 mL of 65% ethanol-water. The solid was recovered by 
filtration and was dried over 18 hours in a 50 degree C. vacuum oven. The 
N-(4-methylsalicyloyl)-8-aminocaprylic acid was isolated as a white solid 
(20.40 g, 52%). 
EXAMPLE 4 
Preparation of 3-(4-(3,5-dichlorosalicyloyl) aminophenyl)propionic acid 
A. Preparation of Oligo(3,5-dichlorosalicylate) 
##STR15## 
3,5-dichlorosalicylic acid (15.00 g, 0.073 mol, 1.0 equiv), acetic 
anhydride (7.69 g, 0.075 mol, 1.04 equiv), and xylenes (40 mL) were added 
to a 100 mL, three neck flask fitted with an argon purge, a magnetic stir 
bar, a thermometer, a Dean-Stark trap, and a cold water condenser. The 
flask was placed into a sand bath, and heating of the cloudy, off white 
reaction mixture was started. At 115.degree. C. the reaction mixture 
cleared and a xylene/acetic acid mixture began to distill into the 
Dean-Stark trap at around 130-135 degrees C. Heating continued until most 
of the xylenes had distilled (approximately 40 mL of liquid was collected) 
and the reaction mixture thickened and became opaque brown in appearance. 
At this point, the temperature of the reaction mixture was 175 degrees C., 
and heating was stopped. The reaction mixture was allowed to cool to room 
temperature and a tan solid was isolated. The tan solid dried under vacuum 
for several days to give 15.3 g of oligo(3,5-dichlorosalicylate). 12.00 g 
of this material was carried on to the next step. 
B. Preparation of Salicyloylamino acid 
##STR16## 
Oligo(3,5-dichlorosalicylate) (12.00 g, 0.070 mol, 1.10 equiv), 
3-(4-aminophenyl) propionic acid (9.42 g, 0.057 mol, 1.0 equiv) and 
dioxane (150 mL) were added to a 500 mL round bottomed flask fitted with a 
magnetic stir bar, an argon purge, and a cold water condenser. A tan 
slurry was formed, and heating was started. The reaction mixture was 
heated at reflux for 3.5 hr. before being allowed to cool to room 
temperature. Dioxane was removed under vacuum leaving a brown residue. The 
brown residue was taken up in aqueous sodium hydroxide (2M, 200 mL). This 
mixture was filtered, extracted with ethyl acetate (350 mL), and acidified 
with 2N hydrochloric acid solution. A tan solid precipitated and was 
isolated by filtration. The tan solid was heated to boiling in a solution 
of ethanol (100 mL) and water (100 mL). Ethanol was then added to the 
boiling mixture until a clear solution was obtained. Activated charcoal 
was added, and the mixture was filtered. Upon cooling a white solid 
precipitated and was isolated by filtration. The white solid was dried 
overnight in a vacuum oven at 50 degrees C. The dried 
3-(4-(3,5dichlorosalicyloyl)aminophenyl)propionic acid was isolated as a 
white solid (9.30 g, 46.0%); mp&gt;225 degrees C.; 'H NMR (DMSO-d6) 612.9 (s, 
IH), 10.6 (s, IH), 8.15 (d, IH), 7.8 (d, 1H), 7.8 (d, 1H), 7.6 (d, 2H), 
7.25 (d, 2H), 2.8 (t, 2H), 2.6 (t, 2H). Anal. Calcd for C16H13C12NO4: C, 
54.24; H, 3.67; N, 3.95. Found: C, 54.21; H, 3.68; N, 3.89. 
The above mentioned patents, applications, test methods, and publications 
are hereby incorporated by reference in their entirety. 
Many variations of the present invention will suggest themselves to those 
skilled in the art in light of the above detailed description. All such 
obvious variations are within the full intended scope of the appended 
claims.