CA1273920A

CA1273920A - Prodrugs of rapamycin

Info

Publication number: CA1273920A
Application number: CA000524469A
Authority: CA
Inventors: Valentino John Stella; Paul Edwin Kennedy
Original assignee: University of Kansas
Current assignee: University of Kansas
Priority date: 1985-12-06
Filing date: 1986-12-03
Publication date: 1990-09-11
Anticipated expiration: 2007-09-11
Also published as: CA1312076C; JPH0670066B2; ATE74134T1; EP0227355A2; GB2183647B; JPS62215592A; DK584886D0; KR940004072B1; JPH0747593B2; AU6608086A; PT83843B; ZA869181B; DE3684574D1; EP0227355B1; DK169409B1; GB2183647A; DK584886A; DK170750B1; PT83843A; US4650803A

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

7~ 3 AHP-8776 PRODRUGS C)F RAPAMYCIN

Ba~k~roun~ Of Ihe ~vention This invention relates to water soluble prodrugs of rapamycin and in particular to certain derivatives of rapamycin such as, for example, the glycinate prodrugs of rapamycin, the propionate prodrugs of rapamycin and the pyrrolidino butyrate prodrugs of rapamycin.
Rapamycin is a known compound described and claimed in United States Letters Pa~ent Nos. 3,929,992, issued December 30, 1975, and 3,993,749 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.

CH~ CH3 OH
H ~CH3 H ~H ~H ~,CH3 H ~H o~NyJ ~ ~H3 CH3 ~ 0~0 1CH--CH2~ ~ OH
CH30 ~H3 CH3 Rapamycin Rapamycin has been disclosed and claimed as useful in the treatment of tumors in Belgian Patent No. 877,700. Rapamycin is, however, only very slightly soluble in water, i.e. 20 micrograms per milliliter, 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. Accordingly9 there is a need in the art for a rapamycin derivati~e 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.

1 -- , 3L~7~

It has now been folmd that water soluble 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 in;ectable composition for the treatment of tumor in humans.

The water soluble prodrugs of this invention comprise mono substituted derivatives at position 28 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 at position 28 of the rapamycin structure having the following configuration.

/
C-(CH2)m~N\

wherein m is an integer from l to 3, wherein Rl and R2 are each hydrogen or an alkyl radical ha,ving 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. 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 Rl 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 derlvatives include those having substituents at both positions 28 and 43 of the rapamycin structure having the same configuration as the substituent for the mono-substituted derivative.

`` ~Z73~
This invention also provides processes for preparing the mono-and di-substituted water soluble prodrugs of rapamycin.

- 2a -~27~Z~ AHP 8776 ~ ccordingly, this invention provides a process for preparing a rapa-mycin derivative mono-substituted at position 2~ or disubstituted at positions 28 and 43 by an acylamino substituent having the configuration /
-C-(CH2)m wherein m is an integer from 1 to 3, wherein Rl and ~2 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 to five carbon atoms; which comprises acylating rapamycin with an acylating agent containing said acylamino substituent having 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 triphenylphosphine 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-wrrolidinopyridine, 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 ~2 7;:i ~2~ AHP-8776 halide (preferrably the acid chloride) a tertiary amine such as pyridin~ or triethylamine is preferred as an acid scavenger type catalyst and a solvent such as anhydrous methylene chloride or chloroform may be used.
In a preferred embodiment the acylation is carried out by reacting rapamycin with an acid of formula O Rl HOC(C~2)mN\ III

in the presence of a coupling agent, e.g. a carbodiimide ~such as dicyclo-hexylcarbodiimide or diisopropylcarbodiimide) or carbonyldiimidazole. A
catalyst such as 4-dimethylaminopyridine or 4-pyrrolidinopyridine is preferred for use with such coupling agents. In such a reaction the acylating agent is understood to be an activated ester formed from the acid of formula III and the carbodiimide 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 Peptidest' 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 1~2 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 ~1 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 manner 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.

~tlf 3~ AHP-8776 The prepRration of typical water soluble prodrugs of rapamycin of this invention is illustrated in the examples which were carried out using the following procedures.
In the examples9 chemical stability studies for rapamycin and the prodrugs were done at 20 ,ug/ml with an ionic strength of 0.5. Stabilities at pH 3.3 (0.05 M acetate buffer) and pH 7.4 (0.05 M phosphate buffer) were studied at 25 and 37.5 C. No 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 ~g/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 ~1 were removed at predetermined times and added to 200 111 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.
~e 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.
Ille liver homogenate studies were done using livers freshly obtained from male albino Sprague-Dawley rats. A 20% liver homogenate was prepared in Sorensen's buffer at p~I 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 llg/ml respectively, at 37.5C.

Rapamycin hydrolysis data in buffers, plasma and in rat liver homogenate are shown in the following table:

~73~

Chemical Stabilit~ Stud~7 A.25C pH tl/2 (hrs) 3.3 35.8 7.D~ 47.~
B.37.5C pH tl/2 (hrs) 3.3 9.9 7.4 10.2 Plasma Stabilit~Z Study (37.5C) A.Human plasma conc (,ug/ml) tl/2 (hrs) B.3~at plasma conc (IJg/ml) tl/2 (hrs)

2.83 C.Liver homogenate conc (llg/ml) tl/2 (hrs) 5.5 In ~11 the prodrug studies, the disappearance of the prodrug peak appeared to result in the formation of a peak with a retention time nearly equalto rapamycin. Analysis of the plasma and homogenate studies by thin layer chromatography (TLC) tended to suggest that rapamycin initially formed but then it further degraded ~o other decomposition products, as does rapamycin itself in these studies.
This invention also 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.

~L273~3~2~ P-8776 ~AMPLE 1 ~ynthesis of Mono-(28)-N,N-Dimethylgl~cinate Ester of Rapamycin In a dry 100 mL round bottom flask was placed 2.80 g (3.07 ~ 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 dicyclohexylcarbodiimide. The flask was 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 stirred overnight at room temperature. A thin layer chromatogram (TLC) of the reaction (solvent system 1:1 acetone:methylene chloride) was taken and 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 off 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 residual 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.

E~AMPLE 2 Synthesis of Methanesulfonic Acid Salt of Mono-(28)-NLN Dimethyl~lycinate Ester of Rapamycin In a dry 11)0 mL round bottom flask was placed 3.00 g (3.10 X 10-3 rnoles) of mono N,N-dimethylglycinate prodrug of rapamycin. This was dissolved in 15 mL of anhydrous methylene chloride (distilled from P2O5). To this was added 2.71 X 10-3 moles~ of a stock solution of methanesulfonic acid dissolved in diethyl llZ 739;Z O AHP-8776 ether. The solvent was immediately removed to give a white solid, wt. 3.25 g, yield 99%. This compound was also found diffieult to recrystallize. The salt form of this compound was found to be unstable to long stirring times. Even in the erystalline form long exposures to light resulted in a slow diseoloration of the material.
Data with respect to mono-(28)-N,N-dimethylglyeinate methanesulfonic aeid salt-prodrug of rapamycin are shown in the following table:

Physical Proe~ties Solubility in water >50 mg/mL

EPLC Operaling Conditions Column RP-18, 150 mm length, 4.6 mm id Preeolumn 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 macroeyclie laetone ring.

Chemical S~ability, 25 C
Conditions tl/2(hrs3 pH 3.3 73 pH 7.4 45 ~7,~ A~[P-8776 Plasma/l~ue Stabili~2 37.5C
Conditions tl/2 (hrs) 50 llg prodrug/mL human plasma 5 50 ,ug prodrug/mL rat plasma 1.8 50 ,ug prodrug/mL liver homogenate 4.5 Plasma/Tissue Stability Study (37.5 C) A. Human plasma conc (~g/ml) tl/2 (hrs) 200 5.6 100 4.8 5.0 B. Rat plasma conc (llg/ml) tl/2 (hrs) ~00 2.5 100 1.8 1.75 C. Liver homogenate conc (llg/ml~ tl/2 (hrs) 4.5 Re~onstitution Procedure The prodrug can be reconstituted with either water for injection or distilled water containing 5% by weight dextrose (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.

~ \
~27~2(~ AlIP-8776 E~AMPLE 3 Sy hesis of Mono-(28)-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 ~10-3 moles~ N,N-diethylaminopropionie acid hydro-chloride salt and 0.50 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 P2O5) was added followed by 15 mg of 4-dimethylaminopyridine. The reaction was stirred overnight at room tempera-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 and 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. The 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 eompound was found difficult to recrystallize and unstable to prolonged e2~posure to light.
NMR (30û MHz, solvent CDCL3~ indicated the spectrum OI the prodrug to be practically identical with that of rapamycin. 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 ~1.2 and ô1.5 which were not found in rapamycin.
Data with respect to mono-(28~-N,N-diethylaminopropionate hydro-chloride salt - prodrug of rapamycin are shown in the following table:

~L273~32g~ AHP-8776 Physical Properties -M.W. 1077 M.P. 99-106 C
Solubility >50 mg/mL in water HPLC Operating 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 Ylow 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-trans isomers as mentioned above for the glycinate prodrug.

Chemical Stabili~
Conditions tl/2(hrs) pH 3.3,25C 33 pH 7.4,25C 17 pH 3.3, 37.5C 7.9 pH 7.4, 37.5C 6.3

3~(~

Pl~sma/Tissue ~tabi3ity, 37.5C
Conditions tl/2(hrs) 50 llg prodrug/mL human plasma 2.5 50 ~Jg prodrug/mL rat plasma 50 ,ug prodrug/mL liver homogenate 3.7 Plasma/Tissue Stability Study (37.5C) A. Human plasma conc (,ug/ml~ tl/2 (hrs) 200 3.25 100 2.15 1 0 50 2.50 B. Rat plasma conc (llg/ml) tl/2 (min) C. Liver homogenate conc (llg/ml) tl/2 (hrs) 3.7 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.

EgAMPLE 4 Synthesis of Mono-(28)-4'-(N-wrrolidino)-butyrate Hydrochloride Salt ~ster of Rapamycin.

In a dry 100 mL round bottom flask was placed 3.50 g (3.83 x 10-3 moles) of rapamycin, 1.48 g (7.66 x 10-3 moles) of 4-wrrolidino-butyric acid hydro-~,7~392~ AHP-8776 chloride salt and 50 mL of anhydrous methylene chloride (distilled from P2Os).
The reaction was placed under a nitrogen atmosphere and 2.50 g (1.21 x 10-2 moles) of dicyclohexylcarbodiimide and 15 mg of 4-N,N-dimethyl-aminopyridine.
The 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. This 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 solid, yield 78%.
Data with respect to the mono-(28)-4'-(pyrrolidino)butyrate hydro-chloride salt-prodrug of rapamycin are shown below:

Ph~sical Properties M.W. 1088 M.P. 94-98 C
Solubility ~15 mg/mL in water 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.

Synthesis of Bis N,N-Dimethy~glycinate Ester of Rapamycin The _-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~limethylglycine, 3.3 eq. of dicyclohe~ylcarbodiimide and 0.16 eq. of 4-N,N-dimethylaminopyridine. After purification on silica gel, ~.Z~3~ AHP-8776 64% of _-glycinate was obtained. NMR confirmed the product with two fi proton singlets for the methyl groups of the two glycinate groups.
The formation of the methane sulfonic acid salt of the _-glycinate 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 products including mainly rapamycin 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 rapamycin can be prepared using as a reagent instead of N,N-dimethyl glycine, glycine, N,N-diethylglycine, N,N-diisopropylglycine, N-propylglycine, 3-aminopropionic acid, N-ethyl-3-aminopropionic acid, 4-aminobutyric acid, N-ethyl-4-amino butyric acid, N,N-dipropyl-4-aminobutyric acid, 2-(N-pyrrolidino) acetic acid, and 3-(N-piperidino) propionic 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. Water soluble derivatives of rapamycin which are disubstituted derivatives at positions 28 and 43 of rapamycin with the substituents 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.

2. A water soluble rapamycin derivative of claim 1 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.

3. The di-substituted derivative of claim 1 wherein the substituents are

4. The di-substituted derivative of claim 1 wherein the substituents are

5. An injectable pharmaceutical composition comprising a pharmaceutically acceptable carrier and a water soluble derivative of rapamycin as defined in claim 1, 2, 3 or 4.

6. A process for preparing a water soluble rapamycin derivative disubstituted at positions 28 and 43 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

7. A process as claimed in claim 6 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 they are attached form a saturated heterocyclic ring having four to five carbon atoms.

8. A process as claimed in claim 6 wherein on the resulting rapamycin the substituents are selected from -CO-CH2N(CH3)2 and -CO-CH2CH2-N(CH2cH3)2.

9. A process as claimed in claim 6 wherein the acylating agent is the acid, the acid halide, the acid anhydride or an activated ester of said acylamino substituent.

10. A process as claimed in claim 9 wherein the acylating agent is the acid of said acylamino substituent in the presence of a coupling agent.

11. A process as claimed in claim 10 wherein the coupling agent is N,N'-dicyclohexylcarbodiimide, 1,1'-carbonyldiimidazole, diethylazodicarboxylate, 2,2'-dithiopyridine, or N,N-diisopropylcarbodiimide.