CA1312076C - Prodrugs of rapamycin - Google Patents

Abstract

Abstract of the Disclosure Water soluble prodrugs of rapamycin are disclosed which are useful as components in injectable pharmaceutical formulations for the treatment of tumors in mammals.

Description

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This invention relE~tes to ~VRter soluble prodrugs of rapamycin Qnd in particular to certain derivatives of raparnycin such as, for example, the glycinate prodrugs of rQpamycin~ the propion~te prodrugs of r~pamycin and the pyrrolidino butyrate prodrugs of rapamycin.
Rapamycin is a known compound described and claimed in Vnited States Letters Patent Nos. 3,929,992, issued December 30, 1975, and 3,9~3,749 issued November 23,1976. Moreover, certain of its acyl derivatives are disclosed and claimed in United States Letters Patent No. 4,316,885, issued February 23,1982.

~113 C~13 OII
, CH3 H ~l H--~CH3 Il ~E~ o~N\l/ ~o O-ClH3 C113 ~- ~) O~lfH--CII2~ ~OII

C1130 ~ J~ C113 Rapulllycin Rapamycin has been disclosed and claimed as useful in the treatment of tumors in Belgian Patent No. 877,700. napamycin is, however, only very slightly soluble in water, i.e. 20 micrograms per millillter, and special injectable formulations have been developed for administration to patients, such as those described and claimed in European Patent Number EP 41,795. These formula-tions are not altogether satisfactory for a number of reasons including toxicity of the carrier. Accordingly, there is a need in the art -for a rapamycin derivative or prodrug which is relatively soluble in water so as to form a safe injectable solution and which is as effective as rapamycin in the treatment of tumors.

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~t has now been found that water soluhle prodrugs of rapamycin can be synthesized which decompose into products including rapamycin in the presence of human plasma and animal tissue homogenates. Such prodrugs of rapamycin provide a component of a valuable pharmaceutical injectable composition for the treatment of tumor in humans.

The water soluble prodrugs of this invention comprise mono-substituted derivatives and disubstituted derivatives at positions 28 and 43 of the rapamycin structure. The assignments are based on a structural elucidation published by Findlay et al in Can. J. of Chem. 58, 579 (1980).

The mono-substituted derivatives include those having a substituent on the rapamycin structure having the following configuration.

/
C~CH2)m~N ~

wherein m is an integer from 1 to 3, wherein Rl and R2 are each hydrogen or an alkyl radical having from one to three carbon atoms or wherein Rl and R2 together with the nitrogen atom to which they are attached form a saturated heterocyclic ring having four or five carbon atoms. Preferred water soluble rapamycin derivatives of the invention are those in which Rl and R2 are each an alkyl radical having from one to three carbon atoms or R1 and R2 together with the nitrogen to which they are attached form a saturated heterocyclic ring having four to five carbon atoms.

The di-substituted derivatives include those having substituents at both positions 28 and ~3 of the rapamycin structure having the same configuration as the substituent for the mono-substituted derivative.

~ - 2 -~ ~.3~2~

This invention also provides processe~ for preparing the mono-and di-substituted water soluble prodrugs of rapamycin.

- 2a -Accordingly, this invention provide~ e7s~for preparing a rapa-mycin derivativ~ mono-substituted or disubstituted at po~itions 28 and 43 by an acylamino substituent having the configuration O R
-c~cH2)mN

wherein m is an integer from 1 to 3, wherein Rl and R2 are each hydrogen or an al;yl radical having from one to three carbon atoms or wherein Rl and R2 together with the nitrogen atom to which they are attached form a saturated heterocyclic ring having four to five carbon atoms; which comprises acylating rapamycin with an acylating agent containing said acylamino substituent having L0 the configuration ll ~R
-C~CH2)mN\

The acylation may be carried out by standard acylation procedures which preferrably foster neutral conditions. The acylating agent may be the acid, the acid halide (i.e. the choride or bromide), the acid anhydride or an activated ester of said acylamino substituent. The acid form of the acylamino substituent is preferred as an acylating agent in the presence of a suitable coupling agent. The particular coupling agent may be most effective in the presence of a catalyst and/or an acid scavenger. Examples of preferred coupling agents and N,N'-dicyclohexylcarbodiimide, l,l'-carbonyldiimidazole, diethylazo~
dicarboxylate, 2,2'-dithiopyridine and N,N-diisopropylcarbodiimide. Diethylazo-dicarboxylate and 2,2'-dithiopyridine require the use of a catalyst such as triphenylphosphine. With these two coupling agents and triphenylphosphlne as a catalyst a non-chlorinated solvent, such as an anhydrous ether, for example tetrahydrofuran, is preferrable. With the other coupling agents the use of an acid scavenger, such as 4-dimethylaminopyridine or 4-pyrrolidinopyridine, is commonly preferred. With the latter coupling agents and catalysts a solvent such as anhydrous methylene chloride or chloroform may be used. With the acid ~ -- 3 --~g ~

2 ~ 7 ~
AMP-~776 halide (preferrably the acid chloride) a tertiary amine such as pyridine or trlethylamine is preferred as an acid scavenger type catalyst and a solvent such as anhydrous methylene chloride or chloroform may be used.
In a preferred ernbodiment the acylation is carried out by reacting rapamycin with an acid of formula /Rl HOl(C112)mN 111 R2 ..
in the presence of a coupling agent, e.g. a carbodiimide (such as dicyclo-hexylcarbodiimide or diisopropylcarbodiimide) or carbonyldiimidazole.
catalyst such as 4~imethylaminopyridine or 4-pyrrolidinopyridine is preferred for use with such coupling agents. ln such a reaction the acylating agent is understood to be an activated ester formed from the acid of formula III and the carbodiirnide coupling agent. Coupling agents including carbodiimides and methods using them are well known in the art since they are extensively used in peptide chemistry--see for example E. Schroder and K. Lubke "The Peptides"
Vol. 1, Academic Press, New York and London 1965 and Mr. Bodanszky and M. A.
Ondetti, Peptide Synthesis 1966 Interscience USA.
Where one or both of Rl and R2 is hydrogen, protection of the amine function of the acylating agent by a protecting group which is removable under neutral conditions is preferred. For example, where one or both of Rl and R2 is hydrogen, the amine function of such acylating agent may be protected by using the acid chloride hydrochloride of the acylamino substituent as the acylating agent. The acid chloride hydrochloride acylating agent may be made in a known rnanner by reacting the acid form of the acylating agent with one equivalent of hydrogen chloride gas then, with one equivalent phosphorous pentachloride.
These reactions may be carried out in anhydrous methylene chloride. The product acid chloride hydrochloride may be recovered as a precipitate or may be precipitated from toluene, hexane or cyclohexane. The acylation using said acid chloride hydrochloride may be carried out in a known manner using a weak base such as pyridine urea, dimethylanaline or trimethylamine as an acid scavenger.

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The preparation of typical water soluble prodrugs of rapamycin of this invent;on is illustrated in the examples which were carried out using the following procedures.
In the examples, chemical stability studies for rapamycin and the prodrugs were done at 20 ~g/ml with an ionic strength of 0.5. Stabilities at pH 3.3 (0.05 M acetate buffer) and pll 7.4 (0.05 M phosphate buffer) were studied at 25 and 37.5 C. ~o antioxidants were added and the buffers were not deoxygenated.
The plasma studies were conducted at 37.5 C for rat and human plasma. Rat plasma was obtained from Sprague-Dawley male albino rats and was used within several days. Human plasma was obtained from the Lawrence Memorial Hospital in Lawrence, Kansas. The plasma studies were done at three prodrug concentrations: 200, 100 and 50 IJg/ml of prodrug. The experimental procedure was as follows: The compound to be tested was taken from a stock aqueous solution of 5 mg/ml and added to the plasma to give the desired prodrug concentration. Samples of 200 111 were removed at predetermined times and added to 200 ~1 of 10% metaphosphoric acid to quench the reaction. Before centrifugation 200 111 of methanol was added to further precipitate the plasma proteins. The results are expressed in half-lives in hours.
The chemical and plasma studies were followed by HPLC using a RP
C-18 column (150 mm) and a precolumn (50 mm). The mobile phase was 87:13 methanol:phosphate buffer (0.025 M, pH 3.4). The detector was set at 254 nm and the flow rate was 1 ml/min for rapamycin studies and 1.5 ml/min for the prodrug studies. Chart speed was 1 inch/10 minutes.
The liver homogenate studies were done uslng livers freshly obtained from male albino Sprague-Dawley rats. A 20% liver homogenate was prepared in Sorensen's buffer at pH 7.4. Chemical stability studies of rapamycin and the two prodrugs of Examples 2 and 3 were carried out at concentrations of 20, 50 and 50 ~g/ml respectivelyJ at 37.5C.
Rapamycin hydrolysis data in buffers, plasma and in rat liver homogenate are shown in the following table:

Chemical Stability Study A.25C pH tl/2 (hrs) 3.3 35.8 7.4 ~7.6 B.37.5C pH tl/2 (hrs) 3.3 9.9 7.4 10.2 Plasma Stability Study (37.5C) A.Human plasma conc ~g/ml) tl/2 (hrs) B.Rat plasma conc (llg/ml) tl/2 (hrs) 2.83 C.Liver homogenate conc (llg/ml) tl/2 (hrs) 5.5 In all the prodrug studies, the disappearance of the prodrug peak appeared to result in the formation of Q peak with a retention time nearly equalto rapamyc;n. Analysis of the plasmu and homogenate studies by thin layer chromatography (TLC) tended to suggest thnt rapamycin initially formed but then it further degraded to other decomposition products, as does rapamycin itself in these studies.
This invention aiso provides an injectable pharmaceutical composition comprising a pharmaceutically acceptable carrier and a water soluble derivative of rapamycin of the invention defined above. Water or any water base carrier known in the art can be used, for example, distilled water, water containing 5%
by weight dextrose (D5W) or a physiologically acceptable salt solution. Such physiologically acceptable salt solution should have a pH in the neutral range, as for example, normal saling or lactated Ringers solutions.

l~XAM~LEl ~31~76 Synthesis of Mono-N,N~Dimethylalycinate Ester of Rapamyc~in In a dry 100 mL round bottom flask was placed 2.80 g (3.07 X 10-3 moles) of rapamycin, 0.616 g (5.98 X 10-3 moles) of N,N-dimethyl glycine and 1.40 g (6~80 x 10~3 moles) of dicyclohexylcarbodiim~de. The flask w~s placed under a nitrogen atmosphere and 60 mL of anhydrous methylene chloride (dried over P20s) was added followed by 60 mg of 4~imethylaminopyridine. The reaction was stlrred overnight at room tèmperature. A thin layer chromatogram (TLC) of the reaction (solvent system 1:1 acetone:methylene chloride) was taken and 0 Indicated the reaction to be complete. The Rf of the monoglycinate prodrug was 0.32. Some bisglycinate was also present at a Rf of 0.09. The reaction was worked-up by first filtering of the dicyclohexylurea (DCU). The solvent was removed on the rotovapor to give a white solid. The crude product was chromatographed on 18 gm of silica gel using 300 mL of ethyl acetate to elute rapamycin plus residu~l DCU. The product was eluted with 1:1 methylene chloride:acetone to give 1.67 g of product, yield 55%. This material was found difficult to recrystallize. NMR (300 MHZ, solvent CDC13) indicated the spectrum of the prodrug to be practically identical to that of rapamycin except for the two singlets arising from the glycinate group. The N,N dimethyl protons appeared as a singlet at ~ 2.32. The methylene group of the glycinate was found at ~ 3.16 as a singlet.

I~AMPLE 2 Synthesis of Methanesulfonic Acid Salt of Mono-N,N-Dimethylqlycln_______er of Rapamycin In a dry 100 mL round bottom flask was placed 3.00 g (3.10 X 10-3 moles) of mono N,N-dimethylglycinate prodrug of rapamycin. This was dissolved in 15 mL of anhydrous methylene chloride (distilled from P2Os). To this was added 2.71 X 10-3 moles) of a stock solution of methanesulfonic acid dissolved in diethyl ~ ~ - 7 ~

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ether. The solvent was immediately removed to give a white solid, wt. 3.25 g, yield 99%. This compound was also lound difficult to recrystallize. The salt form of this compound was found to be unstable to long stirring times. Even in the crystalline form long exposures to light resulted in a slow discoloration of - the material.

Data with respect to mono-N,N-dimethylglycinate methanesulfonic acid salt-prodrug of rapamycin obtaine~ in the above example are shown in the following table.
TABL~2 Physical Properties Solubility in water ~50 mg/mL

HPLC Operaffng Cbnditions Column RP-18, 150 mm length, 4.6 mm id Precolumn 50 mm length, 4.6 mm id Mobile phase 87 parts methanol:l3 parts phosphate buffer ~0.025 M, pH 3.4) Detector Kratos 783 UV 254 nm Flow rate 1.5 mL/min Retention 9.5 mL*

* With a new RP C-18 column two peaks were observed which are believed to be cis-trans isomers about the amide bond in the macrocyclic lactone rin~.

Chemicul Stability, 25 C
Conditions tl/2(hrs) pH 3.3 73 pH 7.4 45 ~ - 8 -.

j!

~ 3 ~

Pl~sma/lgssue S~ability7 ~7.5C
Conditions tl/2 (hrs) 50 IJg prodrug/mL human plasma 5 50 ~g prodrug/mL rat plasma 1.8 50 l~g prodrug/mL liver homogenate 4.5 Plflsma/Tissue Stabilit,y Stu y (37.5 C) A. Human plasma conc (~g/ml) tl/2 (hrs) 200 5.6 100 4.8 5.0 B. Rat plasma conc (,ug/ml) tl/2 (hrs) 200 2.5 100 1.8 1.'15 C. Liver homogenate conc (~Ig/ml) tl/2 (hrs) 4.5 Reconstitution Procedure The prodrug can be reconstituted with either water for injection or distilled wflter contflining 5% by weight dextrose (D5W). 'l'he solutions should be freshly prepared and used immediately (cl hr if possible). 'l'he prodrug appearsto discolor upon prolonged exposure to light. Precaution should be taken to prevent this.

`` 13~L2~7~
E~AMPLE3 Synthesis of Mono-3-(N,N-Diethylamino)propionate Hydrochloride Salt Ester of Rapamycin In a dry 100 mL round bottom flask was placed 1.00 g (1.09 X 10-3 moles) of rapamycin, 0.34 g (2.16 X 10-3 moles) N,N-diethylaminopropionic acid hydro-chloride salt and 0.5û g (2.43 X 10-3 moles) of dicyclohexylcarbodiimide.
The vessel was placed under a nitrogen atmosphere and 25 mL of anhydrous methylene chloride (dried over P2Os) was added followed by 15 mg of 4-dimethylaminopyridine. The reaction was stirred overnight at room tenipera-ture. The next day a TLC of the reaction (solvent system: ethyl acetate) on silanized silica gel plate was taken and indicated the reaction to be complete.
The Rf of the monopropionate hydrochloride salt of rapamycin was 0.34 ~nd 0.01 for the bispropionate hydrochloride salt which was also formed in the reaction.
The dicyclohexylurea was filtered from the reaction and the solvent removed on the rotovapor~ Ihe crude product was chromatographed on 12 g of silanized silica gel. The column was first developed with 200 mL of ethyl acetate to remove any rapamycin and also residual dicyclohexylurea. The product was eluted with ethyl acetate to give 0 61 g of product, yield 53%. This compound was found difficult to recrystallize and unstable to prolonged exposure to light.
0 NMR (300 MHz, solvent CDCL3) indicated the spectrum of the prodrug to be practically identical with that OI rapamycln. The propionate group did not give sharp easily interpreted resonances as was the case with the glycinate prodrug.
This is the result of the resonances being multiplets resulting from the ethyl groups which are not as easily seen among the other resonances from rapamycin.
Broad peaks did appear around 61.2 and 61.5 which were not found in rapamycin.
Data with respect to mono-N,N-diethylaminopropionate hydrochloride salt-prodrug of rapamycin obtained in the above example are shown in the following table:

~, -10-2 ~ ~ ~

Physical Properties M.W. 1077 M.P. 99-106 C
Solubility >50 mg/mL in water HPLC Operatin~ Conditions Column RP-18, 150 mm length, 4.6 mm id Precolumn 50 mm length, 4.6 mm id Mobile phase 87 parts methanol: 13 parts phosphate buffer (0.025 M, pH 3.4) Detector Kratos 783 UV 254 nm Flow rate 1.5 mL/min Retention volume 9.75 mL*

* Two peaks were also observed for this prodrug when a new RP-18 column was used. This was also believed to be cis-trarls isomers as mentioned above for theglycinate prodrug.

Chemical Stabilit,y Conditions tl/2(hrs) pH 3.3,25C 33 pH 7.4,25 C 17 pH 3.3, 37.5C 7.9 pH 7.4, 37.5C 6.3 ~3~ 2~7~
Plasma/Tissue St:ab~lity, 37.5 C
Conditions tl/2~hrs) 50 l~g prodrug/mL human plasma 2.5 50 ~g prodrug/mL rat plasma 50 llg prodrug/mL liver homogenate 3.7 Plasma/Tissue Stability Stu~ ~
A. Human plasma conc (llg/ml) tl/2 (hrs) 200 3.25 100 2.15 L0 50 2.50 B. Rat plasma conc (llg/ml) tl/2 (min) ~0 58 C. Liver homogenate conc (~g/ml) tl/2 (hrs) 3.7 Reconstitution Proceslure The prodrug can be reconstituted with either water for injection or DSW. The solutions should be freshly prepared and used immediately (~1 hr if possible). The prodrug appears to discolor upon prolonged exposure to light.
Precaution should be taken to prevent this.

Synthesis of Mono-4'-~M~yrrolidino)-butyrate Hydrochloride Salt Ester of Rapamycin.

In a dry 100 mL round bottom flask was placed 3.50 g (3.83 x 10-3 moles) of raparnycin, 1.48 g (7.66 x 10-3 moles) of 4-pyrrolidino-butyric acid hydro-~312~7~
chloride salt and 50 mL of anhydrous methylene chloride (distilled from P2Os).
The reaction was placed under a nitrogen atmosphere and ~.50 g (1.21 x lo-2 moles) of dicyclohexylcarbodiimide and 15 mg of 4-N,N-dimethyl-aminopyridine.
l`he reaction was stirred overnight at room temperature. The following day the dicyclohexylurea was filtered from the reaction and the filtrate adsorbed onto 5 g of silanized silica gel. lllis was loaded onto a 12 g column of silanized silica gel and was developed with 75:25 ethyl acetate: hexane to remove the starting material. The product was eluted with ethylacetate to give 3.24 g of a white solld, yield 7896.

LO Data with respect to the mono-4'-(pyrrolidino)butyrate hydrochloride salt-prodrug of rapamycin obtained in the above example are shown below:

Physical Properties M.W. 1088 ~q.P. 94-98 C
Solubility ~15 mg/mL in ~Nater Reconstitution Procedure The prodrug can be reconstituted with either water for injection or D5W. The solutions should be freshly prepared and used immediately (<1 hr if possible). The prodrug appears to discolor upon prolonged exposure to light.
Precaution should be taken to prevent this.

EX~MPI.13 5 Synthesis of Bis N,N-Dimethyl~lycinate Ester of ~apamycin The bis-glycinate prodrug of rapamycin substituted at positions 28 and 43 of the rapamycin structure was synthesized by the addition of 1 eq. of rapamycin, 3 eq. of N,N-dimethylglycine, 3.3 eq. of dicyclohexylcarbodiimide and 0.16 eq. of 4-N,N-dimethylaminopyridine. After purification on silica gel, ;~ ~ - 13 -. ~'`i~l,~
.,r, ~ 3~7~

~HP-8776 64% of bis-glycinate was obtained. NMR confirmed the product with two 6 proton singlets for the methyl groups of the two glycinate groups.
The formation of the methane sulfonic acid salt of the _~lycinate was accomplished by the addition of 1.95 eq. of methane sulfonic acid. The use of two equivalents caused the decomposition of the prodrug. This gave 92% yield of the bis-glycinate prodrug of rapamycin.
The studies carried out using fresh human plasma and fresh rat plasma indicate that the half life of the prodrug of Example 3 was the shortest, i.e. that half of the prodrug decomposed into produets including mainly rapamyein within two and one-half hours with rapamycin being the only observed product of hydrolysis.
Similarly as in Example 1, other water soluble derivatives of rapamyein can be prepared using as a reagent instead OI N,N-dimethyl glyeine, glyeine, N,N-diethylglycine, N,N-diisopropylglyeine, N-propylglycine, 3-aminopropionie acid, N-ethyl-3-aminopropionic acid, 4-aminobutyrie acid, N-ethyl-~-amino butyrie aeid, N,N-dipropyl-4-aminobutyric acid, 2-(N-pyrrolidino) aeetic aeid, and 3-(N-piperidino) propionie acid and using appropriate protecting groups where necessary.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing a water soluble rapamycin derivative mono-substituted by an acylamino substituent having the configuration wherein m is an integer from 1 to 3, wherein R1 and R2 are each hydrogen or an alkyl radical having from one to three carbon atoms or wherein R1 and R2 together with the nitrogen atom to which they are attached form a saturated heterocyclic ring having four to five carbon atoms; which comprises acylating rapamycin with an acylating agent containing the acylamino substituent having the configuration wherein m, R1 and R2 are as defined above, said acylating agent being the acid, the acid halide, the acid anhydride or an activated ester of said acylamino substituent, and the process being effected in the presence of a coupling agent, when required; followed if necessary by acidification to give the pharmaceutically acceptable salt thereof.

2. A process as claimed in claim 1, wherein R1 and R2 of the acylating agent are each an alkyl radical having one to three carbon atoms or R1 and R2 together with the nitrogen to which there are attached form a saturated heterocyclic ring having four to five carbon atoms.

3. A process as claimed in claim 1, wherein the resulting rapamycin is mono-substituted by a substituent selected from -CO-CH2N(CH3)2, -CO-CH2CH2-N(CH2CH3)2, and -CO-CH2CH2CH2-(N-pyrrolidine).

4. A process as claimed in claim 1, 2 or 3, wherein the coupling agent is selected from a N,N-dicyclohexylcarbodiimide, 1,1'-carbonyldiimidazole, diethylazodicarboxylate, 2,2'-dithiopyridine and N,N-diisopropylcarbodiimide.

5. Water soluble mono-substituted derivatives of rapamycin obtained by acylating rapamycin with an acylating agent containing the acylamino substituent having the configuration:
wherein m is an integer from 1 to 3, wherein R1 and R2 is each hydrogen or an alkyl radical having from one to three carbon atoms or wherein R1 and R2 together with the nitrogen to which they are attached form a saturated heterocyclic ring having four to five carbon atoms and the pharmaceutically acceptable salts of such derivatives, when prepared by the process defined in claim 1 or a chemical equivalent thereof.

6. A water soluble rapamycin derivative of claim 5, wherein R1 and R2 are each an alkyl radical having from one to three carbon atoms or R1 and R2 together with the nitrogen to which they are attached form a saturated heterocyclic ring having four to five carbon atoms.

7. The mono-substituted derivative of claim 5, wherein the substituent is 8. The mono-substituted derivative of claim 5, wherein the substituent is 9. The mono-substituted derivative of claim 5, wherein the substituent is 10. An injectable pharmaceutical composition comprising a pharmaceutically acceptable carrier and a water soluble derivative of rapamycin as defined in claim 5, 6, 7, 8 or 9.