CA2317736C

CA2317736C - Bisulfate salt of hiv protease inhibitor

Info

Publication number: CA2317736C
Application number: CA002317736A
Authority: CA
Inventors: Janak Singh; Madhusudhan Pudipeddi; Mark D. Lindrud
Original assignee: Bristol Myers Squibb Co
Current assignee: Bristol Myers Squibb Holdings Ireland ULC
Priority date: 1998-01-20
Filing date: 1998-12-22
Publication date: 2004-11-02
Anticipated expiration: 2018-12-22
Also published as: DE69806067D1; HUP0101389A2; EE04434B1; SK10622000A3; SK283975B6; LT2000067A; CZ20002564A3; NO20003692D0; ZA9956B; CZ293507B6; IL137384A0; GEP20033026B; PL190744B1; HUP0101389A3; DK1056722T3; BG104618A; ES2178300T3; UY25345A1; PL342019A1; EP1056722B1

Abstract

The present invention provides the crystalline bisulfate salt of formula (II) which is found to have unexpectedly high solubility/dissolution rate and oral bioavailability relative to the free base form of this azapeptide HIV protease inhibitor compound.

Description

1. Field of the Inventi n The present invention provides the novel crystalline bisulfate salt of the azapeptide HIV protease inhibitor of the formula N
H OH ~ O
H
H3C0 ~ ~ N' ~ OCH3 O H O
I
which exhibits unexpectedly superior aqueous solubility/dissolution behavior compared to other salts, and significantly improved oral bioavailability in animals compared to the free base. The bisulfate salt is thus useful for pharmaceutical dosage forms of the above-indicated protease inhibitor, particularly oral dosage forms.

2. Backg round Art Published PCT patent application WO 97/40029 discloses a series of azapeptide HIV protease inhibitors reported to have a high degree of inhibitory activity against the HIV virus. One of the agents included within the scope of WO 97/40029 is the compound having the structural formula GI/O 99!36404 PCTNS98lZ738z N
_ _. ~' E ~ OH p H
1W~ iV. N~ OChi,~
H3C '10 o H o I
and the chemical name [3S-(3R'~, 8'R'~, 9'R;, 12R*)]-3,12-bit~(1,1-dimethylethyl)- 8-hydro~;y-4,11-cl.ivxo~9-(pheny!methyl)-6-[[4-(2~pyridinyl)-phenylmethyl~-2,5,6,1Q,1;Z-pentaazatetradecaanediaic acid, dimefihyl estez and is under evaluation ~~s a possible second generation H:IV protease inhibitor.
WO 99JqOp29 disc~~oses they free base farm of azapeptide derivatives such as compound I and also vaxxous pharmaceutically acenptable acid addition salts. While several or8;anic and inorganic acids are mentior<ed ;t.s possible salt-formin; agents, itxciuding sulfuric add, there is no ~xtention of the particular bisulfate salt which is the subj~t of the presexit ~~pplication.
S~~F THE INVENTION
The present invention prov~ide5 the bisulfate salt of compound I
t~bove having the structural formula N' \
/ \
H OH ~ O
H3C0 N~ N, Nu OCH3 . HzS04 H O H ~ 'IO
B

3 BRIEF DESCRIPTION OF THE DRAWINGS
Figure I shows the solubility of the free base Compound I in water as a function of pH
at a temperature of 24 ~ 3°C.

Figure IIa shows the solid state physical stability of the bisulfate salt (Compound II) as measured by differential scanning calorimetry when stored at 40°C175% relative humidity for nine months, compared to storage of the same material at 2-8°C in closed a container.
Figure IIb shows the solid state physical stability of the hydrochloride salt of Compound I as measured by differential scanning calorimetry when stored at 40°C/75% relative humidity for two weeks compared to storage of the same material at 2-8°C in a closed container.
Figure IIc shows the solid state physical stability of the methane sulfonate salt of Compound I as measured by differential scanning calorimetry when stored at 40°C175% relative humidity for two weeks compared to storage of the same material at 2-8°C in a closed container.
Figure IId shows the solid state physical stability of the sulfate salt of Compound I as measured by differential scanning calorimetry when stored at 40°C/75%
relative humidity for two weeks compared to storage of the same material at 2-8°C in a closed container.

4 DETAILED DESCRIPTION OF THE INVENTION
Compound I as disclosed above is a weak organic base with an aqueous solubility of less than 1 ~,g/mL at 24 ~ 3° C. The crystalline free base form as a suspension in water or oil has poor oral bioavailability in animals, probably b~.ause of its extremely Iow solubility in these vehicles.
For development of pharmaceutical formulations, particularly oral dosage forms, the active ingredient must have sufficient oral bioavailability. Since the free base form of compound I did not possess such bioavailability, acid addition salts were explored by the present inventors. A number of commonly used acid addition salts such as the hydrochloride, benzenesulfonate, methanesulfonate, p-toluenesulfonate, phosphate, nitrate, 1,2-ethanedisulfonate, isethionate and sulfate were evaluated, in addition to the bisulfate salt of the present invention. All of these salts in their crystalline form exhibited lower aqueous solubility (1-3 mg/mL or less at 24 ~ 3° C) than the bisulfate which had a solubility under the same conditions of approximately 4-5 mg/mL.
Solid state transformation was observed when the other acid addition salts mentioned above were suspended in water, probably due to their dissociation to form the free base. In the majority of cases, this transformation was accompanied by gel formation. Unlike the other salts mentioned above, the extra proton of the bisulfate salt prevents the conversion to the free base which, as mentioned above, is very insoluble in water and has poor oral bioavailability. The unusual solubility JUL . 5 . 2000 1 '- 18Pf1 BMSiPfaTENTS C FR7C#609252d526 ) NO. 108 P . 2i8 'ali0 99!36404 PGTNS9811'~38Z
, behavior of the bisulfate salt in water is further elaboratec; in the followizig.
In general, conversion of salts to the unionized forW or vice versa

5 can be explained on the basis of pH~solubility theory. The solubility of the free base in water was dnterminfld as a function of pH at 29. ~ 3° C
and is shown below. The pH eat which the eoxnpound exhibits the highest solubility is referred to a,~ pHm"~ ,~tnd was Found to be approximately 1.2..
It has been reported in the literatw~e that at pH ? pH~"sY of a ~nreakly basfc organic compound, the ~~qu9J.ibrium solid phase in an agu~~ous suspension of the compound is the free base. At pH < pHm,x the equilibrium solid converts to the correspandiztg se~lt form, The term "equilibrium solid phase" refers to the undissolved or excess solid in a suspension of the compound in water after sufficient equilibration time. Wlten a salt of a weak base is equilibrated in watE:r in as amount exceeding its solubility limit (i.e., a suspension of~the salt in water), the resulting pH of the suspension may fall on either side of the pH"",x depending on the strength of the acid among artier t°actors. When the resulting pH is greater than the pH""x. the suspended solid converts to the free base.
Studies conducted with methane sulfonate and hydrochloride salts, in particular, of the free base confirmed the above described general findings reported in the literature. Amounts in excess of the solubility of these salts were equilibrated in water at 24 ~ 3~ C for at least 24 hours. The pH of the suspensions after equilibration was 2.1 ~ 0.1 which is greater than the pH~x. The undissolved solids from these suspensions were isolated, air-dried, and characterized. By thermal and elemental analysis the undissolved solids from these suspensions were identified as the free base. This behavior was expected based on the pH-solubility profile shown in the graph above and the studies reported in the literature.

6 When an excess amount of the bisulfate salt was equilibrated in water a modification occurred in the solid phase in equilibrium with solution. However, the undissolved solid phase after equilibration was not the free base, although the pH (1.9 ~ 0.2} of the suspension was greater than the pH~ and comparable to the pH of the suspensions of methane sulfonate and hydrochloride salts described above. The solid phase after at least 24 hours of equilibration was identified by elemental analysis as a hydrated form of 2:1 salt of the free base form and sulfuric acid (referred to as the sulfate salt). This behavior of the bisulfate salt is l o unexpected based on pH-solubility theory.
When an excess amount of the sulfate salt, in turn, was equilibrated in water a modification occured in the solid phase in equilibrium with solution. The undissolved solid from this suspension was isolated, air-15 dried, and characterized. Thermal and . elemental analysis of this undissolved solid phase was similar to that of the free base although the conversion of the sulfate salt to the free base was not as definitive as that of the methane sulfonate and hydrochloride salts. From a pharmaceutical point of view the propensity of salts to convert to the free base in an 20 aqueous environment is not desirable due to the low oral bioavailability of the free base. Thus, the bisulfate salt due its unique solubility behavior in water offered unexpected superiority.
The solubility behavior of the bisulfate salt in water was also 25 expected considering the interaction of compound I free base and sulfuric acid in water. For example, the free base exhibited a solubility of less than 1 mg/mL in water at a pH of --1.8 adjusted with sulfuric acid, compared to ~-5 mg/ml., solubility of the bisulfate salt in vuater at comparable pH canditio.ns. Basiyd on pH-solubility theory the free base 30 and the salt are expected. to exhibit similar solubility at a given pH_ The enhanced solwbility/.dissolutifln behavior of the bisulfate contributes to its improved oral bioavailability in animals relarive to the free base. The absolute oral bioavailability of the bisulfate salt was found 35 tq be approximately 20%~ in dogs when administered in, umformulated solid form placed in a gelatin calasule. 1.n comparison, the Cryst811it1e free base had minimal ozal bi oavailalaility in dogs.

'j~l'O 99/36404 PCTNS981Z~38Z

7 In addition to optimal soh~bility, satisfactory physical stability in the solid-state is another desixable pn~operty of pharmaceutical ,salt forms. The term physical stability indicates the ability of the salt form co retain its crystal structure (includir~g solvents .of crystallization, if azl.y) under storage/stress conditions. Significant changes in the physical xtature of the .salt form as irrdieated by thermal methods such as differen~xal scarwing ~calorimetry are uxidesirab le. The bisulfate salt exhibited ex~.Glaeht solid-~5tate physical stability when store~.d at ~0°C/75°/°
relative humidity (I~ for - as long as 9 months as shown in l.?a below. Dif;Eerential sca;nrting ~alorimetry revealed no signif~tcamt changes in the thermal behavior of Lhe stressed sample of the bisulfal:e salt compared to that of the ur<.stressed ~;~ample (stored at 2-8°C in a closed container)_ The methaw.
sulfonate, ~tydrochloride, and the sulfate salts, on the other hand, sho~Ned significant changes in their thermal behavior when stared at 40°C/75%RH for as 1!ittle as two weeks as shovrrt in II 'b, c, azi.d d. while differences in physical t~tability of salt forms is ncrt unusual, the propervsity of a parlieular salt to form solvates (or crystal ntodificaitions) aztd its ability to retain the solvent of czystallizatiort (the physical stattility of crystal modifications) under storage/stress conditions cannot bn predicted apriori.
The bisulfate szlt may be p~~epared by (orating a solution of free base c;~f compound I with sulfuric acid in solvents such as acetonitrile, a~~opropanol, ethanol, or acetone and then isolating the so-p;uduced lyisulfate salt.
Because of its high hioavaihlbility as well as its good crystallinity rind stability, the bisulfate salt is v~~r~r useful in preparing oral dosage If~rms of compound I. 1'he examples which follow illusncat~a preparation ~f representative oral forinulatior~s.
The bisulfate salt, amd formulations thereof, are used F4s described in '4~~T0 97/40029 for the treat~n~nt of diseases caused by vixuses, especially a~~tro~riruses such as the ITV viruu;,

8 DESCRIPTION OF SPECIFIC EMBODIMENTS
Example 1 'reparation of Bisulfate Salt From Ethanol To a 500 mL three-necked round bottomed flask equipped with an overhead stirrer and dropping funnel,15.013 g (0.0213 mole) of free base compound I and 113 mL of 200 proof ethanol were added with stirring. To.
this suspension,1.28 mL concentrated sulfuric acid was added dropwise over 90 seconds. After the addition of sulfuric acid, a clear amber-colored solution was obtained. The solution was polish filtered using #1 Whatman filter paper and washed with 5 mL of 200 proof ethanol. To this solution was added 58 mL of heptane and 37.5 mg (0.25 wt %) of seed crystals of the compound of formula II followed by 55 mL of additional heptane. The resulting mixture was stirred for 6 hours at 300 rpm. The resulting crystal slurry was filtered and washed with 50 mL
ethanol/heptane (1:1) solution and dried under vac-sum at ~60° C
overnight to afford 15.11 g of the desired crystalline bisulfate salt (88.4 mole % yield) having formula II above.
Characterizing P~nerties of Bisulfate Salt Anal. Calcd. for C3gH52N60 . 1.0 H2S04 : C, 56.84; H, 6.78; N,10.37; S, 3.99.
Found: C, 56.72; H, 6.65; N,10.41; S, 3.83.
m.p. 195.0°
H20 = 0.28% (KF) Vi~'y7 99/36404 PCTlU598n?38Z

9 t.xa~pie 2 Pre~rarat~.i~on of 8j~,~ulfate Salt FXQm~C~.~!:
SM H2S0ø (8.52 mL, 42.6 mIvl) vas added dzvpwfse ~co a suspension of the free base compour"d of for,cnula I (30.0 g-, 42.6 mM) i~ acetone (213 mL) stirred mechanically in a 50"C oil-bath. ,A. clear solution was obtained alnnost immediately. T'hy solution was seeded with crystals of the free base compound of formv,la II. After two minutes, a precipitate formed which became a paste. The mixtlare was stirred at 50°C for one hour, at 25°C for 30 minutes and ;it 0°C fair 2 hours_ The solid was filtered and the tsrst filtrate was used to ~xansfer the reuiafning material in the flask to the filtration funnel. The prs~duct was washed with acetone, then heptane, and dried under vacuum overnight to give 31.48 g (eorrectEtd yield 929'0) of the bisulfate salt of formv.la JI, m.p. 198-199°C dec.
,Anal. Calcd. CssH52NsO7.1.0 H25~4.0~ Fi20 : C, 56.59; H, 6,80; N,10.42; S, s.9s; H2o, 0.45.
,Found: C, 56.66; H, d.78;1J.10.50; S, 4.20; H20, 0,45 (KF).
~xa Prevaratfon.of~~fa. to Sal~~tom IsQpt~~
Aqueous sulfuric acrid (5.0 Poi, 0.z0 mL, 1 mM) was a.d~~ed to a ;3uspettsion of the free base compt~und of formula I (0.704 g, 1.00 rnM) in i~sopropanol (4.0 mL) chilled in am ice bath. The ice-bath w~is removed and 'the mixture stirred a~~ room temperature. The susperts:4on had dissolved after 15 minutesi. The s~dlution was seeded wifih crystals prepared as irf Examples 1 or 2 above aztd stirred for 5 hourt~. The solid -tntas filtered and the filtrate was u,~ed to transfer the solid from the flask to the funnel. The product was washed with heptane and dried under ~racuum to give 0.752 g oi~ crystalline bisulfate salt of forznuia II, yield 90%, ~rnp_ 160-190°C, dee. ' WO 99136404 PC'T1US98/17382 Anal. Calcd. for C3gH52N60~.1.0 H2SO4.2.0 H20; C, 54.40; H, 6.97; N,10.02;
S, 3.82; H20, 4.29.
Found: C, 54.25; H, 6.73; N, 10.02; S, 3.67; H20, 4.53 (ICS.
5 The crystals obtained from isopropanol showed a powder x-ray diffraction pattern different from the crystals obtained from acetonitrile, - ethanol-heptane or acetone. They are now referred to as Type-II crystals.
The Type-I crystals appear to be an anhydrous/desolvated crystalline material while the Type-II crystals are a hydrated, hygroscopic crystalline

10 form.
Example 4 Preparation of Capsule Formulations of Bisulfate Salt A. Capsules (50 and 200 mg free base equivalent) Capsules are provided for oral administration in which the capsule is a size #0, gray, opaque, hard gelatin capsule containing the bisulfate salt of formula II formulated as a wet granulation with lactose, crospovidone and magnesium stearate.
B. Capsules (100 mg free base equivalent) Capsules are provided for oral administration in which the capsule is a size #0, gray, opaque, hard gelatin capsule containing the bisulfate salt of formula II suspended in Gelucir~ 44/14. Gelucire 44/14 is a saturated polyglycolized glyceride consisting of mono-, di- and triglycerides and mono- and di-fatty acid esters of polyethylene glycol.
Capsules are prepared by melting Gelucire 44/14 at 45-70° C
followed by addition of the bisulfate salt with stirring. The molten mixture is filled into hard gelatin capsules and allowed to cool and solidify.
* trade-mark

Claims

We claim:

1. The bisulfate salt having the formula

2. A pharmaceutical dosage form comprising the bisulfate salt of Claim 1 and a pharmaceutically acceptable carrier.