US20020013311A1

US20020013311A1 - Aniline disulfide derivatives for treating allergic diseases

Info

Publication number: US20020013311A1
Application number: US09/841,898
Authority: US
Inventors: Mark Hellberg; Zixia Feng; Steven Miller
Original assignee: Alcon Universal Ltd
Current assignee: Novartis AG
Priority date: 2000-05-19
Filing date: 2001-04-25
Publication date: 2002-01-31
Anticipated expiration: 2021-04-25
Also published as: AR028565A1; DE60104690T2; BR0110845A; CA2408145A1; HK1050677A1; AU2001257227B2; US6452052B1; PT1289945E; ZA200208839B; MXPA02011480A; CN1429208A; EP1289945B1; DE60104690D1; ES2222370T3; TR200402299T4; WO2001090059A1; KR20020093982A; AU5722701A; DK1289945T3; ATE272619T1

Abstract

Methods and compositions for preventing or treating allergic diseases of the eye, nose, skin, ear, gastrointestinal tract, airways or lung and preventing or treating manifestations of systemic mastocytosis are disclosed. The compositions contain a mast cell stabilizing disulfide derivative as an active ingredient.

Description

This application claims priority from co-pending U.S. Provisional Application, U.S. Ser. No. 60/205,746, filed May 19, 2000.[0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the treatment of allergic diseases. More particularly, the present invention relates to therapeutic and prophylactic use of certain disulfide derivatives for treating or preventing allergic diseases.

2. Description of the Related Art

Antihistamines and mast cell stabilizers are two types of drugs currently used topically to treat allergic diseases. Antihistamine drugs are used to interrupt the allergic effects that histamine causes after it has been released from a mast cell. Many topical antihistamine drugs are marketed. For example, emedastine difumarate and levocabastine hydrochloride are available for ocular allergies (see Ophthalmic Drug Facts 1999, Facts and Comparisons, St. Louis, Mo., pp. 59 - 80).

Mast cell stabilizers prevent mast cells from “degranulating” or releasing histamine and other components or “mediators” during an allergic reaction. Examples of ophthalmic drugs marketed as mast cell stabilizers include olopatadine (see U.S. Pat, No. 5,641,805) and cromolyn sodium.

U.S. Pat. No. 4,705,805 discloses certain disulfide derivatives that are useful as anti-thrombotic agents. The disulfide derivatives suppress blood platelet aggregation. The '705 patent does not disclose the use of disulfide derivatives in the treatment of allergic diseases.

SUMMARY OF THE INVENTION

The present invention provides methods for preventing or treating allergic diseases of the eye, nose, skin, ear, gastrointestinal tract, airways or lung. The methods may also be used to treat manifestations of systemic mastocytosis. The methods of the present invention comprise topically or systemically administering to a patient a mast cell stabilizing disulfide derivative of the formula

wherein

X is —NH—C (═O)—R, or —NH—C(═O)—OR;

R=H; (un)substituted phenyl; (un)substituted benzyl; or C ₁-C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5 - 7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R²;

R ²=C₁-C₃alkyl; and

R ³and R⁴are independently H; benzyl; C₁-C₈alkyl or alkenyl; C₄-C₇cycloalkyl; (un)substituted aryl; or (un)substituted 5 - 7 membered heterocyclic ring; wherein optional substituents are selected from the group consisting Of C_1-C ₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

The present invention is also directed toward topically or systemically administrable compositions for treating or preventing allergic diseases of the eye, nose, skin, ear, gastrointestinal tract, airways or lung and treating or preventing manifestations of systemic mastocytosis, wherein the compositions comprise a disulfide derivative of formula (I).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to novel disulfide derivatives of formula (I) wherein

X is —NH—C(═O)—R;

R is —C(—R ⁵)—C═C(—R⁶)R⁷or —C(—R⁵)—C(—OH)R⁶;

R ⁵is H, C₁-C₃alkyl;

R ⁶is H, C₁-C₃alkyl or alkenyl; and

R ⁷is H, C₁-C₄alkyl or alkenyl.

The remaining disulfide derivatives of formula (I) are known or are commercially available from sources such as Aldrich Chemical Company (Sigma Aldrich Library of Rare Chemicals) in Milwaukee, Wis. and Maybridge Chemical Company Ltd. in the U.K. The novel and known disulfide derivatives of formula (I) can be made using known techniques, such as those described in Domagala J M et al. Biorganic and Medicinal Chemistry volume 5 No. 3 pages 569-79 (1997), and U.S. Pat. No. 4,705,805 (Yamotsu K. et al., 1987). The entire contents of both of these references are incorporated by reference.

Preferred compounds of formula (I) are those wherein the X substituents are in the ortho position and wherein

X=—NH—C(═O)—R; and

R=C ₁-C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

Most preferred are compounds wherein R=C ₁-C₅alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

Compounds of formula (I) may be administered topically (i.e., local, organ-specific delivery) or systemically by means of conventional topical or systemic formulations, such as solutions, suspensions or gels for the eye and ear; nasal sprays or mists for the nose; metered dose inhalers for the lung; solutions, gels, creams or lotions for the skin; oral dosage forms including tablets or syrups for the gastrointestinal tract; and parenteral dosage forms including injectable formulations. The concentration of the compound of formula (I) in the formulations of the present invention will depend on the selected route of administration and dosage form. The concentration of the compound of formula (I) in topically administrable formulations will generally be about 0.00001 to 5 wt. %. For systemically administrable dosage forms, the concentration of the compound of formula (I) will generally range from about 10mg to 1000mg.

The preferred formulation for topical ophthalmic administration is a solution intended to be administered as eye drops. For solutions intended for topical administration to the eye, the concentration of the compound of formula (I) is preferably 0.0001 to 0.2 wt. %, and most preferably from about 0.0001 to 0.01 wt. %. The topical compositions of the present invention are prepared according to conventional techniques and contain conventional excipients in addition to one or more compounds of formula (I). A general method of preparing eye drop compositions is described below: One or more compounds of formula (I) and a tonicity-adjusting agent are added to sterilized purified water and if desired or required, one or more excipients. The tonicity-adjusting agent is present in an amount sufficient to cause the final composition to have an ophthalmically acceptable osmolality (generally about 150-450 mOsm, preferably 250-350 mOsm). Conventional excipients include preservatives, buffering agents, chelating agents or stabilizers, viscosity-enhancing agents and others. The chosen ingredients are mixed until homogeneous. After the solution is mixed, pH is adjusted (typically with NaOH or HCI) to be within a range suitable for topical ophthalmic use, preferably within the range of 4.5 to 8.

Many ophthalmically acceptable excipients are known, including, for example, sodium chloride, mannitol, glycerin or the like as a tonicity-adjusting agent; benzalkonium chloride, polyquaternium-1 or the like as a preservative; sodium hydrogenphosphate, sodium dihydrogenphosphate, boric acid or the like as a buffering agent; edetate disodium or the like as a chelating agent or stabilizer; polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, polysaccharide or the like as a viscosity-enhancing agent; and sodium hydroxide, hydrochloric acid or the like as a pH controller.

If required or desired, other drugs can be combined with the disulfide derivatives of formula (I), including, but not limited to, antihistaminic agents, anti-inflammatory agents (steroidal and non-steroidal), and decongestants. Suitable antihistaminic agents include emedastine, mapinastine, epinastine, levocabastine, loratadine, desloratadine, ketotifen, azelastine, cetirazine, and fexofenadine. The preferred antihistaminic agent for ophthalmic use is emedastine, which is generally included in topically administrable compositions at a concentration of 0.001-0.1 wt. %, preferably 0.05 wt. %. Suitable anti-inflammatory agents includemometasone, fluticasone, dexamethasone, prednisolone, hydrocortisone, rimexolone and loteprednol. Suitable decongestants include oxymetazoline, naphazoline, tetrahydrozoline, xylometazoline, propylhexedrine, ethylnorepinephrine, pseudoephedrine, and phenylpropanolamine.

According to the present invention, the disulfide derivatives of formula (I) are useful for preventing and treating ophthalmic allergic disorders, including allergic conjunctivitis, vernal conjunctivitis, vernal keratoconjunctivitis, and giant papillary conjunctivitis; nasal allergic disorders, including allergic rhinitis and sinusitis; otic allergic disorders, including eustachian tube itching; allergic disorders of the upper and lower airways, including intrinsic and extrinsic asthma; allergic disorders of the skin, including dermatitis, eczema and urticaria; allergic disorders of the gastrointestinal tract, including systemic anaphylaxis resulting from ingestion of allergen and iatrogenic anaphylaxis caused by contrast agents used during diagnostic imaging procedures; and manifestations of systemic mastocytosis including hypotension.

The following examples are intended to be illustrative but not limiting.

EXAMPLE 1: TOPICAL OPHTHALMIC SOLUTION FORMULATION



	Ingredient	Concentration (wt. %)

	Compound of formula (I)	0.0001 to 0.2
	Dibasic Sodium Phosphate (Anhydrous)	0.5
	Sodium Chloride	0.65
	Benzalkonium Chloride	0.01
	NaOH/HCl	q.s. pH 6-8
	Purified Water	q.s. 100

EXAMPLE 2: TOPICAL OPTHALMIC GEL FORMULATION



	Ingredient	Concentration (wt. %)

	Compound of formula (I)	0.0001 to 0.2
	Carbopol 974 P	0.8
	Edetate Disodium	0.01
	Polysorbate 80	0.05
	Benzalkonium Chloride	0.01
	NaOH/HCl	q.s. pH 6-8
	Water for Injection	q.s. 100

EXAMPLE 3: SYNTHESIS OF BIS-(2-ALLYLAMIDOPHENYL)-DISULFIDE (II)

Vinylacetic acid (1.97 ml, 23.23 mmol) in thionyl chloride (2.7 ml, 34.85 mmol) was gently refluxed on an oil bath (˜80° C.) for two hours. After cooling, the liquid was evaporated on a rotary evaporator. The residue was dissolved in 20 ml of dioxane. 2-aminophenyl disulfide (Aldrich, 1.44g, 5.8 mmol) in 10 ml of dioxane was added and the resulting mixture was cooled to 10° C. Triethylamine (7 ml, 50 mmol) was added slowly under nitrogen. After addition, the mixture was stirred at 10° C for 1 hr and 700° C. for 2 hr. After cooling, the solids were filtered off and the filtrate was concentrated. The residue was dissolved in 50 ml of CH[0034] ₂CL₂, washed with 1 N HCL, (20 ml), saturated NaHCO₃(20 ml), water (20 ml) and saturated NaCL (20 ml) and then dried over MgSO₄. The mixture was filtered and the solvent was concentrated. The residue was chromatographed on silicon gel eluting with 50% of ethyl acetate in hexane), giving 0.71 g of product which was solidified as yellowish solid (II). ¹H NMR (CDCL₃) δ 9.73 (s, 2H), 7.63-7.18 ( m, 8H), 6.21-5.90 (m,2H), 5.27-513 (m, 4H), 3.16-3.13 (d, 4H, J=6.0). ¹³C NMR (CDCL₃) δ 169.74 (C═O), 136.43 (C), 132.57 (CH), 131.94 (C), 129.52 (CH), 128.59 (CH), 126.92 (CH), 126.36 (CH), 118.38 (CH₂), 40.95 (CH₂). Analysis calculated for C₂₀H_{20 O} ₂N₂S₂requires: C, 62.47; H, 5.24; N, 7.28%. Found, C, 62.40; H, 5.28; N, 7.20%.

EXAMPLE 4: SYNTHESIS OF BIS-(2-(3-HYDROXY-BUTYRYLAMIDO)PHENYL)-DISULFIDE

To a solution of 2-aminophenyldisulfide (1.5 g, 6 mmol) was added a solution of 3-hydroxy-butyric acid (2.5 g, 24 mmol) in THF (8 ml) at 0° C. while stirring. To this mixture was added dicyclohexylcarbodiimide (4.95g, 24mmol). After stirring at 5 ° C. or 1 h, the mixture was stirred overnight at room temperature. The solvent was evaporated on a rotavapor. Ethyl acetate (50 ml) was added to the residue and washed with water (3×20ml) and saturated NaCL (20 ml) and then dried over MgSO[0035] ₄. The mixture was filtered and the solvent was concentrated. The residue was chromatographed on silicon gel eluting with 50% of ethyl acetate in hexane), giving 0.31 g of product as white solid. ¹H NMR (CDCL₃) δ 7.80-7.76 (m, 2H), 7.48-7.43 (m, 2H), 7.37-7.29 (m, 2H), 7.14-7.07 (m, 2H), 4.22-4.13 (m, 2H), 2.46-2.42 (m, 4H), 1.27-1.24 ( d, 6H, J=6.0). ¹³C NMR (CDCL₃) δ 172.88 (C═O), 139.42 (C), 134.60 (CH), 131.08 (CH), 130.11 (C), 126.96 (CH), 125.49 (CH), 65.77 (CH), 46.68 (CH₂), 23.56 (CH₃). ESI LC/MS [M+H]⁺:421.

EXAMPLE 5: MAST CELL ACTIVITY

Preparation of cell suspension [0036]
Methods detailing preparation of monodispersed HCTMC and mediator release studies with these cells have been described (U.S. Pat. No. 5,360,720 and Miller et al, Ocular Immunology and Inflammation, 4(1):39 - 49 (1996)). Briefly, human conjunctival tissue mast cells were isolated from post-mortem tissue donors obtained within 8 hours of death by various eye banks and transported in Dexsol® corneal preservation medium, or equivalent. Tissues were enzymatically digested by repeated exposure (30 min. at 37° C.) to collagenase and hyaluronidase (2 ×with 200 U each / gram tissue, then 2-4× with 2000 U each / gram tissue) in Tyrode's buffer containing 0.1% gelatin. (Tyrode's buffer (in mM): 137 NaCL, 2.7 KCL, 0.35 NaH[0037] ₂PO4, 1.8 CaCL₂, 0.98 MgCL₂, 11.9 NaHCO₃, and 5.5 glucose). Each digestion mixture was filtered over Nitex® cloth (100 μm mesh, Tetko, Briarcliff Manor, N.Y.) and washed with an equal volume of buffer. Filtrates were centrifuged at 825×g (7 min). Pellets were resuspended in buffer then combined for enrichment over a 1.058 g/L Percoll® cushion. The enriched pellet was washed, resuspended in supplemented RPMI 1640 medium and incubated at 37° C. to equilibrate.
Histamine release studies [0038]
Cells were harvested from the culture plate and counted for viability (trypan blue exclusion) and mast cell number (toluidine blue O). Mast cells (5000 / tube; 1 mL final volume) were challenged (37° C.) for 15 min with goat-anti-human IgE (10 μg/mL) following treatment (15 minutes; 37° C.) with test drug or Tyrode's buffer. Total and non-specific release controls were exposed to 0.1% Triton X-100 and goat IgG (10 μg/mL), respectively. The reaction was terminated by centrifugation (500×g, 4° C., 10 min). Supernatants were stored at −20° C. until analyzed for histamine content by RIA (Beckman Coulter, Chicago, Ill.). [0039]
Preparation of test drug solutions [0040]
All test drugs were made to solution immediately prior to use. Each was dissolved in DMSO at 10 mM or greater concentration and then diluted in Tyrode's buffer containing 0.1% gelatin over the concentration for evaluation. [0041]
Data Analysis [0042]

Inhibition of histamine release was determined by direct comparison of with anti-IgE challenged mast cells using Dunnett's t-test (Dunnett, “A multiple comparison procedure for comparing treatments with a control”, J. Amer. Stat. Assoc. (1955), 50:1096-1121). An IC50 value (the concentration at which the test compound inhibits histamine release at a level of 50% compared to the positive control) was determined by 4-parameter logistic fifting using the Levenburg-Marquardt algorithm or by linear regression. The results are reported in Table 1.


COMPOUND
NO.	T	X	MOLSTRUCTURE	IC50 (nM)


1.	S—S	85 27 [56]

2.	S—S	656 306 [481]

3.	S—S	690 292 [491]

4.	S—S	3180 <1000

5.	S—S	174 2200 [1187]

6.	S—S	1700

[0044] 0
The data shown in Table 1 indicate that the compounds of formula (I) potently inhibit histamine release from human conjunctival mast cells in an in vitro model of allergic conjunctivitis. [0045]

EXAMPLE 6: TOPICAL OPHTHALMIC SOLUTION FORMULATION



	Ingredient	Concentration (wt. %)

	Compound of formula (I)	0.0001 to 0.2
	Emedastine	0.001 to 0.1
	Dibasic Sodium Phosphate (Anhydrous)	0.5
	Sodium Chloride	0.65
	Benzalkonium Chloride	0.01
	NaOH/HCl	q.s. pH 6-8
	Purified Water	q.s. 100

The invention has been described by reference to certain preferred embodiments; however, it should be understood that it may be embodied in other specific forms or variations thereof without departing from its spirit or essential characteristics. The embodiments described above are therefore considered to be illustrative in all respects and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description. [0047]

Claims

What is claimed is:

1. A method for preventing or treating an allergic disease of the eye, nose, skin, ear, gastrointestinal tract or lung and preventing or treating manifestations of systemic mastocytosis in a patient comprising administering

to the patient a composition comprising a disulfide derivative of the formula

wherein

X is —NH—C(═O)—R, or —NH—C(═O)—OR;

R and R¹are independently H; (un)substituted phenyl; (un)substituted benzyl; or C₁-C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R²;

R²is C₁-C₃alkyl; and

R³and R⁴are independently H; benzyl; C₁-C₈alkyl or alkenyl; C₄-C₇cycloalkyl; (un)substituted aryl; or (un)substituted 5-7 membered heterocyclic ring; wherein optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

2. The method of claim 1 wherein the X substituents are in the ortho position and wherein

X=—NH—C(═O)—R; and

R=C₁-C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

3. The method of claim 2 wherein R=C₁-C₅alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

4. The method of claim 3 wherein X is selected from the group consisting of —NH—C(═O)—CH₂CH═CH₂; —NH—C(═O)—CH₃; —NH—C(═O)—C(═CH₂)—CH₃; —NH—C(═O)—CH₂—CH(—OH)—CH₃; —NH—C(═O)—O—CH₂—CH₃; and —NH—C(═O)—C(CH₃)₃.

5. The method of claim 1 wherein the disulfide derivative is administered to the patient in a topically administrable composition containing the disulfide derivative in an amount from about 0.00001 to 5 wt. %.

6. The method of claim 5 wherein the disulfide derivative is present in an amount from about 0.0001 to 0.2 wt. %.

7. The method of claim 6 wherein the disulfide derivative is present in an amount from about 0.0001 to 0.01 wt. %.

8. The method of claim 1 wherein the disulfide derivative is administered to the patient in a systemically administrable composition containing the disulfide derivative in an amount from about 10 to 1000 mg.

9. A topically or locally administrable pharmaceutical composition for treating allergic diseases of the eye, nose, skin, ear or lung comprising a tonicity-adjusting agent in an amount sufficient to cause the composition to have an osmolality of 150-450 mOsm, a pharmaceutically acceptable preservative and a disulfide derivative of the formula

wherein

X is —NH—C(═O)—R, or —NH—C(═O)—OR;

R and R¹are independently H; (un)substituted phenyl; (un)substituted benzyl; or C₁-C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR²;NR³R⁴; —C₄—C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5 - 7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁- C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R²;

R²is C₁-C₃alkyl; and

R³and R⁴are independently H; benzyl; C₁- C₈alkyl or alkenyl; C₄-C₇cycloalkyl; (un)substituted aryl; or (un)substituted 5 - 7 membered heterocyclic ring; wherein optional substituents are selected from the group consisting of C₁- C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

10. The pharmaceutical composition of claim 9 wherein the X substituents are in the ortho position and wherein

x=—NH—C(═O)—R; and

R=C₁- C₈alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴; C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁- C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

11. The pharmaceutical composition of claim 10 wherein R=C_{1 - C} ₅alkyl or alkenyl, optionally substituted with or terminated by OH, OR², NR³R⁴, C₄-C₇cycloalkyl, (un)substituted aryl, or (un)substituted 5-7 membered heterocyclic ring; where optional substituents are selected from the group consisting of C₁-C₆alkyl or alkoxy; halogen; OH; CN; CF₃; NO₂; and CO₂R².

12. The pharmaceutical composition of claim 11 wherein X is selected from the group consisting of —NH—C(═O)—CH₂CH═CH₂; —NH—C(═O)—CH₃; —NH—C(═O)—C(═CH₂)—CH₃; —NH—C(═O)—CH₂—CH(—OH)—CH₃; —NH—C(═O)—O—CH₂—CH₃; and —NH—C(═O)—C(CH₃)₃.

13. The pharmaceutical composition of claim 9 wherein the disulfide derivative is present in an amount from about 0.00001 to 5 wt. %.

14. The pharmaceutical composition of claim 13 wherein the disulfide derivative is present in an amount from about 0.0001 to 0.2 wt. %.

15. The pharmaceutical composition of claim 14 wherein the disulfide derivative is present in an amount from about 0.0001 to 0.01 wt. %.

16. A disulfide derivative of the formula

wherein

X is —NH—C(═O)—R;

R is —C(—R⁵)—C═C(—R⁶)R⁷or —C(—R⁵)—C(—OH)R⁶;

R⁵is H, C₁-C₃alkyl;

R⁶is H, C₁- C₃alkyl or alkenyl; and

R⁷is H, C₁- C₄alkyl or alkenyl.

17. The disulfide derivative of claim 16 wherein R is —C(—R⁵)—C═C(—R⁶)R⁷and R⁵, R⁶, and R⁷are H.

18. The disulfide derivative of claim 16 wherein R is —C(—⁵)—C(—OH)R⁶, R⁵is H, and R⁶is CH₃.