Tryptophan derivatives

The invention provides certain substituted tryptophan derivatives of Formula I which are useful for alleviating or reducing angiotensin related hypertension in hypertensive mammals.

BACKGROUND OF THE INVENTION 
The present invention provides novel compounds. In particular the present 
invention relates to novel tryptophan derivatives of formula I which are 
useful for reducing or relieving angiotensin related hypertension. 
Angiotensin II is a powerful vasoconstrictor agent that has been implicated 
as the main causative agent in the etiology of renovascular hypertension. 
Angiotensin II is formed from angiotensin I by the action of angiotensin 
converting enzyme. Angiotensin I is a biologically inert decapeptide 
cleaved from the blood protein angiotensinogen by the action of the enzyme 
renin [Oparil et al., New England J. of Med., 291, 389-401 (1974)]. 
Angiotensin converting enzyme and renin are also biologically inert. 
Angiotensin converting enzyme is also responsible for the inactivation of 
bradykinin, a vasodilator agent that has been implicated in the regulation 
of renal function [Erdos, Circulation Research 36,247 (1975)]. 
Agents that inhibit angiotensin converting enzyme can therefore counteract 
the indirect pressor effect of angiotensin I since this is due only to its 
conversion to angiotensin II. These agents can be used therapeutically in 
the treatment of forms of renovascular and malignant hypertension as well 
as other forms of angiotensin dependent hypertension [Gavras et al., New 
England J. of Med., 291 817 (1974)]. 
According to Oparil et al, supra, angiotensin II has a major role in 
maintaining circulatory homeostasis in the sodium depleted animal, but in 
the normal animal on a normal salt intake, angiotensin II is not required 
for the acute maintenance of blood pressure. In a variety of conditions 
that stress the renin-angiotensin system, acute administration of an 
Angiotensin Converting Enzyme inhibitor or an angiotensin II blocker 
lowers blood pressure and causes a rise in plasma renin activity. 
Certain mercaptoacyl amino acids have been disclosed in the literature. 
U.S. Pat. No. 3,246,025, Apr. 12, 1966, shows mercatopropionyl glycine 
derivatives which are useful for strengthening function of the liver and 
as antidotes for such poisons as mercury and organoarsenic compounds. See 
also German Offenlegungsschriff No. 2,349,707, U.S. Pat. No. 3,897,480, 
July 29, 1957 shows N (.alpha.-mercaptoacyl)amino acids useful for 
prophylaxis and therapy in treating a metabolic disorder, such as 
nosotoxicosis due to a heavy metal, radiation disorder, diabetes or 
hepatitis, U.S. Pat. No. 3,857,951, Dec. 31, 1974, shows the use of 
2-mercaptopropionylglycine and its alkali metal salts in treating 
respiratory diseases. 
It has been reported that 2-mercaptopropionyl glycine, known as a liver 
protecting agent, produced lowering of the blood pressure upon intravenous 
injection to anesthetized normotensive rats [Schulze, Arznem Forsch, 22, 
1433 (1972)], an unreliable model [Schwartz, Methods in Pharmacology, Vol. 
I, 125 (1971); Berger, Selected Pharmacological Testing Methods, Vol. 3, 
171, 194 (1968)]; while others have reported no noticeable effects on 
blood pressure, etc. [Fujimura et al., Nippon Yakurigaku Zasshi 60, 278, 
92 (1964)]. See also Ripa, Proc. Int. Symp. Thiola, Osaka, Japan 1970, p. 
226-230, who reported that in normotensive rats mercaptopropionylglycine 
increases angiotensinogen and lowers renin blood levels by a feedback 
homeostatic mechanism. 
A variety of dipeptides are known as shown in the text Pettit, Synthetic 
Peptides, Vol. I (1971), e.g., pages 94-104. Additionally, foodstuff 
additives are shown, for example, in the following U.S. Pat. Nos. 
2,851,482, L-argininyl-L-glutamate; 3,799,918, alkyl esters of 
.alpha.-aspartyl-.alpha.-alkyl aliphatic amino acid dipeptides; 3,952,115, 
N-acyl-L-methionine ester, N,N'-diacyl-L-glycylmethionine and 
methionylglycine; and 4,024,286, dipeptides of methionine with glycine, 
valine, alanine or glutamic acid. 
PRIOR ART 
Pharmacologically active compounds for treating hypertension are known as 
described above. Additionally, in U.S. Pat. No. 4,177,277 a method for 
alleviating hypertension in mammals by administration of an amino acid 
derivative is described. Further, Japanese Pat. Nos. 089215 (Derwent 
Abstract 19283C/1) and 082809 (Derwent Abstract 09529C/06) describe 
mercapto-amino acids which are useful as antihypertensives. 
SUMMARY OF THE INVENTION 
The present invention particularly provides a compound according to formula 
I: 
wherein R.sub.1 is: 
(a) hydrogen; or 
(b) methyl; 
wherein R.sub.2 is: 
(a) hydrogen; 
(b) iso-propyl; or 
(c) tert-butyl; 
wherein R.sub.3 is: 
(a) methyl; or 
(b) NR.sub.5 H; 
wherein R.sub.5 is: 
(a) hydrogen; or 
(b) aroyl; 
wherein R.sub.4 is: 
(a) CH.sub.2 SH; 
(b) iso-propyl; 
(c) iso-butyl; 
(d) imidazolmethyl; 
(e) phenylmethyl; or 
(f) methylthioethyl. 
The blocking of the conversion of Angiotensin I to Angiotensin II is a 
known powerful method of controlling certain forms of hypertension. The 
following two procedures are used in the rat to test for in vivo 
converting enzyme blocking activity and therefore antihypertensive 
activity of the invention compounds. These procedures have been verified 
through the testing of the known converting enzyme blocker Captopril. 
Two normotensive rats at a time were anesthetized with 1.5 g/kg urethane IM 
and cannulated with Tygon tubing (0.040".times.0.025") via the left 
carotid for blood pressure monitoring. The right jugular vein was doubly 
cannulated (Tygon 0.030".times.0.010") for Angiotensin I injections and 
for the test compound. The rats were tracheotomized and cardiovascular 
reflexes blocked with pentolinium tartrate (5 mg/kg i.m.). 
Procedure 1 
Infusion of Compound 
Following surgery the animals were allowed to stabilize for 30 minutes. 
Three challenge doses of Angiotensin I (500 ng/kg i.v. in a volume of 0.01 
ml/100 g) were administered at three minute intervals before treatment to 
establish the diastolic blood pressure responses. After reestablishing a 
baseline BP the test compound was infused for a 10 min. period at a rate 
of 0.05 ml/min. Probe dosing with Angiotensin I was repeated 2,4, and 8 
minutes after starting the infusion. If the response to AI was not 
abolished by the initial 10 minute infusion, the rate of infusion is 
doubled (0.1 ml/min) and maintained for an additional ten minutes. The AI 
challenges were repeated 2, 4 and 8 minutes into the second infusion 
period. Rates higher than 0.1 ml/min were not used. At the end of the 
infusion the probe doses of AI were given at 5 min intervals for 30 
minutes to estimate the rate of inactivation of the compound. 
Procedure 2 
Bolus Injections 
The animals were surgically prepared as described in Procedure 1 and 
allowed to stabilize for 30 min. Pretreatment blood pressure responses to 
injections of AI (500 ng/kg i.v.) were obtained before administration of 
test compound. After recovering to base line a bolus injection of the test 
compound was given. Probe dosing with AI was done at 2, 5, 10 min after 
the antagonist injection. Twelve minutes after the first injection a 
predetermined higher dose of the drug was given and the probe dosing of AI 
were repeated. This sequence is repeated for a total of three doses of the 
drug. In some animals two doses of AII (200 ng/kg) were given before the 
start of the AI injections and after completion of the sequence to test 
for specificity of the response. 
By virtue of this antihypertensive activity the compounds of formula I are 
useful in treating hypertensive symptoms in humans and animals. A 
physician or veterinarian of ordinary skill could readily determine a 
subject who is exhibiting hypertensive symptoms. Regardless of the route 
of administration selected, the compounds of the present invention are 
formulated into pharmaceutically acceptable dosage forms by conventional 
methods known to the pharmaceutical art. 
The compounds can be administered in such oral unit dosage forms as 
tablets, capsules, pills, powders, or granules. They also may be 
administered rectally, or vaginally in such forms as suppositories, 
creams, ointments or bougies; they may also be introduced in the form of 
eye drops, intraparenterally, subcutaneously, intramuscularly, or 
intravenously, using forms known to the pharmaceutical art. 
An effective but non-toxic quantity of the compound is employed in 
treatment. The dosage regimen for preventing or treating hypertension by 
the compounds of this invention is selected in accordance with a variety 
of factors including the type, age, weight, sex, and medical condition of 
the mammal, the severity of the hypertension, the route of administration 
and the particular compound employed. An ordinarily skilled physician or 
veterinarian will readily determine and prescribe the effective amount of 
the anti-hypertensive agent to prevent or arrest the progress of the 
condition. In so proceeding, the physician or veterinarian could employ 
relatively low dosages at first, subsequently increasing the dose until a 
maximum response is obtained. 
Initial dosages of the compounds of the invention are ordinarily in the 
area of 0.3 mg/kg up to at least 100 mg/kg orally. When other forms of 
administration are employed equivalent doses are administered. When 
dosages beyond 100 mg/kg are employed, care should be taken with each 
subsequent dose to monitor possible toxic effects. 
The compounds of this invention can also be administered as 
pharmacologically acceptable acid addition salts such as the 
hydrochloride, hydrobromide, hydroiodide, sulfate, phosphate, acetate, 
propionate, lactate, maleate, malate, succinate, tartrate and the like. 
Additionally, the compounds of this invention may be administered in a 
suitable hydrated form. 
The compounds of the instant invention are all prepared by the methods 
described in Charts A and B. 
The thio compound of the instant invention is prepared as described on 
Chart A. DL-S-Acetyl-.beta.-mercaptoisobutyric acid and N-methylmorpholine 
are cooled and isobutylchloroformate added. Then Val-Trp-methylester is 
added and the solution reacted, cooled and extracted to yield the formula 
II trytophan methylester. The formula II ester is then treated with a 
basic alcoholic solution and concentrated. The residue is then extracted 
to yield a formula III tryptophan derivative. 
Chart B describes the process for producing the amino derivatives of the 
invention A t-butyl-oxycarbonyl-Val and N-Methyl-morpholine is reacted 
with isobutylchloroformate and then with L-Trp-methylester hydrochloride. 
This reaction yields the tryptophan methylester of formula XI. The formula 
XI methylester is then treated with anhydrous hydrochloric acid to yield 
the tryptophan methylester hydrochloride of formula XII. 
A solution of t-butyloxycarbonyl-L-Leu and N-methylmorpholine is treated 
successively with isobutylchloroformate and the formula XII methylester to 
yield the formula XIII methylester. This methylester is then hydrolyzed in 
a basic alcoholic solution to yield the formula XIV tryptophan derivative. 
This can be treated with anhydrous acid to yield the formula XV tryptophan 
derivative. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS

The operation of this invention is further elaborated by the representative 
examples below: 
EXAMPLE 1 
t-butyloxycarbonyl-Valyl-tryptophan methyl ester (formula XI of Chart B: 
R.sub.2 is isopropyl) 
A tetrahydrofuran solution (60 ml) containing 3.4 g. (15.7 mmoles) of 
t-butyloxycarbnyl-Val and 3.3 ml (29.4 mmoles) of N-methylmorpholine is 
cooled to -20.degree. C. and 1.9 ml (14.8 mmoles) of isobutylchloroformate 
is added. The resulting suspension is stirred at -20.degree. C. for 5 
minutes and 2.8 g (11.0 mmoles) of L-Trp-OCH.sub.3 -HCl is added. After 
stirring the reaction at -20.degree. C. for 3 hours, it is allowed to warm 
to room temperature and stirred overnight. It is then cooled to 0.degree. 
C. and stirred for 30 minutes with 2 molar KHCO.sub.3 and extracted with 
ethyl acetate. The organic layer is washed successively with 5 percent 
citric acid, water and saturated sodium chloride, then dried over a 
magnesium sulfate. Upon concentrating under reduced pressure, a solid is 
obtained which is crystallized from isopropanol to give 3.15 g (68 
percent) of title compound. Structure supported by NMR. 
EXAMPLE 2 
Valyl-tryptophan methyl ester.HCl (formula XII of Chart B: R.sub.2 is 
isopropyl). 
A 3.1 g (7.43 mmoles) sample of the product of Example 1 is dissolved in 20 
ml of acetic acid and treated with 11.3 ml (74.6 mmoles) of 6.6 N HCl in 
dioxane. After stirring the solution 10 minutes at room temperature, it is 
concentrated under reduced pressure at 40.degree. C. and the residue 
obtained is triturated with ether to give 2.6 g (99 percent) of title 
compound. Analysis calculated for C.sub.17 H.sub.20 N.sub.3 O.sub.2 HCl is 
C, 57.70; H, 6.84; N, 11.88. Found: C, 57.75; H, 6.84, N, 11.71. Structure 
supported by NMR. 
EXAMPLE 3 
t-butyloxycarbonyl-Leu-Val-Trp-methyl ester (formula 3 of Chart B: R.sub.2 
is isopropyl; R.sub.4 is isobutyl). 
A tetrahydrofuran solution (60 ml) containing 2.6 g (10.4 mmoles) of 
t-butyloxycarbonyl-L-Leu(H.sub.2 O) and 2.2 ml (19.6 mmoles) of 
N-methyl-morpholine is cooled to -20.degree. C. and 1.26 ml (9.68 mmoles) 
of isobutylchloroformate is added. The resulting suspension is stirred at 
-20.degree. C. for 5 minutes and 2.6 g (7.37 mmoles) of title compound of 
Example 2 is added. After stirring the reaction at -20.degree. C. for 3 
hours, it is allowed to warm to room temperature and is stirred for an 
additional 2 hours. It is then cooled to 0.degree. C., stirred for 30 
minutes with 2 molar KHCO.sub.3 and extracted with ethyl acetate. The 
organic layer is washed successively with 5 percent citric acid, water and 
saturated sodium chloride, dried over magnesium sulfate and concentrated 
under reduced pressure to give 3.9 g (100 percent) of title compound. 
EXAMPLE 4 
t-butyloxycarbonyl-Leucyl-Valyl-tryptophan (formula XIV of Chart B: R.sub.2 
is isopropyl; and R.sub.4 is isobutyl). 
A 3.0 g (5.66 mmoles) sample of title compound of Example 3 is dissolved in 
12 ml of 95 percent ethanol and treated with 6 ml of 1 N sodium hydroxide. 
After stirring the solution at room temperature for 4 hours, it is 
concentrated under reduced pressure. The residue is dissolved in water, 
and the basic solution extracted with ether. The aqueous layer is 
acidified with 5 percent citric acid and extracted with ethyl acetate. The 
organic phase is washed with saturated sodium chloride solution, dried 
over a magnesium sulfate and concentrated under reduced pressure to give 
2.6 g (90 percent) of the title compound. 
EXAMPLE 5 
Leucyl-Valyl-tryptophan hydrochloride (formula I of Chart A: R.sub.1 is 
hydrogen; R.sub.2 is isopropyl; R.sub.3 is NH.sub.2 ; R.sub.4 is 
isobutyl). 
To a 1.8 g (3.49 mmoles) sample of title compound Example 4 in 10 ml of 
glacial acetic acid is added 5.3 ml (35.0 mmoles) of 6.6 N HCl in a 
dioxane. The solution is stirred at room temperature for 10 minutes and 
concentrated under reduced pressure at 40.degree. C. The residue is 
triturated with ether to give 1.4 g (89 percent) of the title compound. 
EXAMPLE 6 
N-[S-acetyl-.beta.-mercaptoisobutyroyl]-valyl-tryptophan methyl ester 
(formula II of Chart A: R.sub.2 is isopropyl). 
A tetrahydrofuran solution (250 ml) containing 5.5 g (34.0 mmoles) of 
DL-S-Acetyl-.beta.-mercaptoisobutyric acid and 7.7 ml (68.6 mmoles) of 
N-methylmorpholine is cooled to -20.degree. C. and 4.2 ml (32.3 mmoles) of 
isobutylchloroformate is added. The suspension is stirred at -20.degree. 
C. for 5 minutes and 10.0 g (28.3 mmoles) of Val-Trp-methylester HCl is 
added. After stirring the reaction at -20.degree. C. for 2 hours at room 
temperature an additional 2 hours, it is cooled to 0.degree. C., stirred 
for 30 minutes with 2 molar KHCO.sub.3 and extracted with ethyl acetate. 
The organic layer is washed successively with 5 percent citric acid, 
water and saturated sodium chloride, dried over magnesium sulfate and 
concentrated under reduced pressure to give 11.5 g (88 percent) of title 
compound. 
EXAMPLE 7 
N-[N-(3-mercapto-2-methyl-1-oxopropyl)valyl]tryptophan (formula 1 of Chart 
A: R.sub.1 is hydrogen; R.sub.2 is isopropyl; R.sub.3 is methyl; R.sub.4 
is HSCH.sub.2). 
A 5.5 g (11.9 mmoles) sample of the title compound of Example 6 is 
suspended in 95 percent ethanol (70 ml) and treated with 35 ml of 1 N 
sodium hydroxide. After stirring the reaction at room temperature for 4 
hours it is concentrated under reduced pressure. The residue is dissolved 
in water and the basic solution extracted with ether. The aqueous layer is 
acidified with 10 percent HCl and extracted with ethyl acetate. The 
organic phase is washed with saturated sodium chloride solution, dried 
over magnesium sulfate and concentrated under reduced pressure. Following 
chromatography, one obtains 3.5 g (73 percent) of title compound. 
EXAMPLE 8 
N-[N(3-mercapto-2-methyl-1-oxopropyl)glycylm]tryptophan. 
The title compound is prepared using the previously described procedures 
and the following reagants 3.0 grams (7.16, mmoles) 
N-(S-acetyl-.beta.-mercaptoisobutyroyl)-glycyl-tryptophan methyl ester, 40 
ml 95 percent ethanol, 21 ml 1 N NaOH. Yield total 1.1 gram (42 percent). 
Analysis calculated for C.sub.17 H.sub.21 N.sub.3 O.sub.4 S: C, 56.18; H, 
5.82; N, 11.56; S 8.82. Found: C, 55.77; H, 5.80; N, 11.44; S, 8.87. 
EXAMPLE 9 
L-Leucyl-L-3-methyl-valyl-L-tryptophan hydrochloride. 
The title compound is prepared using the previously described procedures 
and the following reagants: 0.45 grams (0.85 mmoles) 
t-butyloxcarbonyl-leucyl-3-methyl-valyl-tryptophan, 2.8 ml glacial acetic 
acid, and 1.4 ml of 6.07 N HCl in dioxane. Yield was 0.27 grams (67 
percent). Analysis calculated for C.sub.23 H.sub.34 N.sub.4 
O.sub.4.HCl.H.sub.2 O: is C, 56.96; H, 7.69; N, 11.55 found C, 57.26; H, 
7.55; N, 11.16. 
EXAMPLE 10 
N-[N-(3-mercapto-2-methyl-1-oxopropyl)-3-methyl-valyl]tryptophan. 
The title compound is prepared using the previously described procedures 
and the following reagants: 0.90 g (1.89 mmoles) of 
N-(S-acetyl-.beta.-mercaptoisobutyroyl)-3-methylvalyl-tryptophan methyl 
ester, 8 ml of 95 percent ethanol, 4.0 ml of 1 N NaOH. Chromatographed 
yield is 0.54 grams (63 percent). Analysis calculated for C.sub.21 
H.sub.29 N.sub.3 O.sub.4 S: C, 60.12; H, 6.97; N, 10.02; S, 7.64. Found: 
C, 60.27; H, 7.14; N, 9.42; S, 7.25. 
EXAMPLE 11 
L-Phenylalanyl-valyl-tryptophan hydrochloride. 
The title compound is prepared using the previously described procedures 
and the following reagants: 1.85 grams (3.4 mmoles) 
t-butyloxycarbonyl-phenylalanyl-valyl-tryptophan, 10 ml of glacial acetic 
acid and 7.25 ml of 6.07 N hydrochloric acid in dioxane. Yield is 1.6 g 
(100 percent). Analysis calculated for C.sub.25 H.sub.30 N.sub.4 
O.sub.4.HCl.2H.sub.2 O: C, 56.99; H, 6.93; N, 9.17. Found: C, 56.70; H, 
6.43; N, 8.82. 
EXAMPLE 12 
L-Methionyl-L-valyl-L-tryptophan hydrochloride. 
The title compound was prepared using the previously described procedure 
and the following reagants: t-butyl oxycarbonyl-methionyl-valyl-tryptophan 
(4.61 grams), 32 milliliters of glacial acetic acid and 17.5 ml (106.2 
mmoles) 6.07 N hydrochloric acid in dioxane. Yield is 3.2 grams. Analysis 
calculated for C.sub.21 H.sub.30 N.sub.4 O.sub.4 S.HCL.H.sub.2 O: C, 
51.57; H, 6.80; N, 11.46. Found: C, 51.29; H, 6.59; N,-11.72. 
EXAMPLE 13 
.gamma.-[(methylsulfinyl)-L-.alpha.-aminobutyroyl-valyl]-L-tryptophan 
hydrochloride. 
To a solution containing 1.0 grams (2.05 mmoles) of 
methionyl-valyl-tryptophan in 16 milliliters of water is added 0.8 ml of 
10.4 N H.sub.2 O.sub.2 solution (8.4 mmoles). The solution is stirred at 
room temperature for two hours and eluted with 75 ml of water. Solution is 
then lyopholized to give 0.60 grams (56 percent) of the title compound. 
Analysis calculated for C.sub.21 H.sub.30 N.sub.4 O.sub.5 S.HCl.2H.sub.2 
O: C, 48.22; H, 6.74; N, 10.71. Found: C, 48.34; H, 6.64; N, 11.32. 
EXAMPLE 14 
.beta.-(methylthio-.alpha.-aminopropionoyl-valyl)-trytophan hydrochloride 
The title compound was prepared using the previously described procedures 
and the following reagants: 2.37 grams (4.56 mmoles) 
t-butyloxycarbonyl-5-methylcysteinyl-valyl-tryptophan, 14.7 ml glacial 
acetic acid and 8 ml of 6.07 N HCl in dioxane total yield was 1.7 g (82 
percent). Analysis calculated for C.sub.20 H.sub.28 N.sub.4 O.sub.4 S.HCl: 
C, 52.5; H, 6.40; N, 12.26. Found: C, 52.73; H, 6.62; N, 11.95. 
EXAMPLE 15 
L-Histidyl-L-valyl-L-tryptophan dihydrochloride. 
A 5.0 g (0.9 mmoles) sample of t-butyloxycarbonyl-histidyl-valyl-tryptophan 
methyl ester, which was prepared using the processes previously described, 
in 10 ml 1 N HCl is heated on a steam bath for two hours. The solvent is 
removed under reduced pressure and the residue dissolved in acetic acid 
and precipitated with ether. Yield of a solid was 0.44 grams (96 percent). 
Purified by counter current distribution in butyl alcohol, acetic acid and 
water to obtain 0.34 grams of the title compound. Analysis calculated for 
C.sub.22 H.sub.28 N.sub.6 O.sub.4.2HCl.13/4 H.sub.2 O: C, 48.49; H, 6.20; 
N, 15.42. Found: C, 48.27; H, 5.81; N, 15.25. 
EXAMPLE 16 
L-Valyl-valyl-tryptophan hydrochloride 
The title compound was prepared using the previously described process 
using the following reagants: 0.85 grams (1.7 mmoles) 
t-butyloxycarbonyl-Valyl-valyl-tryptophan, 6 ml glacial acetic acid and 3 
ml 5.68 N HCl in dioxane Total yield was 0.75 grams (100 percent). 
Anaylsis calculated for C.sub.21 H.sub.30 N.sub.4 O.sub.4.HCl.1/3 H.sub.2 
O: C, 56.69; H, 7.17; N, 12.59. Found: C, 57.06; H, 7.3; N, 12.17. 
EXAMPLE 17 
L-Isoleucyl-L-valyl-L-tryptophan hydrochloride. 
The title compound is prepared using the previously described procedures 
and the following reagants: 1.17 g (2.3 mmoles) 
t-butyloxycarbonyl-isoleucyl-valyl-tryptophan, 10 ml glacial acetic acid 
and 10 ml 6.07 HCl in dioxane. Total yield was 0.91 g. (88 percent). 
Analysis calculated for C.sub.22 H.sub.32 N.sub.4 O.sub.4.HCl. H.sub.2 O: 
C, 56.10; H, 7.49, N, 11.90. Found: C, 56.34; H, 7.48; N, 11.72. 
EXAMPLE 18 
Benzoyl-phenylalanyl-valyl-tryptophan. 
A mixture of 30 ml chloroform and 30 ml water containing 1.0 g of 
phenylalanyl-valyl-tryptophan and 0.6 g of sodium carbonate is cooled to 
0.degree. and treated with 0.20 ml of benzoyl chloride. The reaction 
mixture was allowed to warm to room temperature and stirred overnight. The 
layers were separated and the aqueous layer extracted with ethyl acetate. 
The combined organic phases were dried over magnesium sulfate and 
concentrated under reduced pressure to give 0.47 g (53 percent) of the 
title compound. Analysis calculated for C.sub.32 H.sub.34 N.sub.4 
O.sub.5.H.sub.2 O: C, 67.11; H, 6.34; N, 9.79. Found: C, 67.00; H, 6.23; 
N, 9.13. 
EXAMPLE 19 
Using the previously described processes and appropriate starting materials 
the following compounds may be prepared. 
Benzoyl-methionyl-valyl-tryptophan 
N-Benzyl-cysteinyl-valyl-tryptophan 
##STR1##