Sulfonylurea derivatives of oleanolic acid

Description

BACKGROUND

1. Field

The disclosure of the present patent application relates to compounds exhibiting anti-diabetic activity, and particularly to sulfonylurea derivatives of oleanolic acid.

2. Description of the Related Art

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia. The American Diabetes Association suggests that by the year 2030, over 350 million people worldwide will be afflicted with this disease and its complications. In Type II DM, a patient's body develops insulin resistance, resulting in hyperglycemia. At present, four types of chemical drugs, including sulfonylureas, biguanides, α-glucosidase inhibitors and euglycemic agents, are used clinically for the treatment of Type 2 DM. Oleanolic acid is a natural triterpenoid, which has been shown to lower blood glucose. The sulfonylureas have been shown to increase insulin release from the pancreas.

Recent developments in anti-diabetic treatment have focused on replacing insulin injections with oral treatment, as well as on increasing the potency and duration of available anti-diabetic agents.

Thus, oleanolic acid sulfonylurea derivatives solving the aforementioned problem are desired.

SUMMARY

The sulfonylurea derivatives of oleanolic acid include compounds replacing the 5-chloro-2-methoxybenzoic acid moiety found in glibenclamide with oleanolic acid. The resulting triterpenoidal sulfonylurea derivatives are compounds having the following formula:

or a pharmaceutically acceptable salt thereof. The derivatives are synthesized by condensation of 3-oxo-Olean-12-en-28-oic acid with 4-(2-aminoethyl)benzenesulfonamide to form an intermediate product, followed by reaction with cyclohexyl isocyanate or 4-methylcyclohexyl isocyanate to give 3a or 3b, respectively. The sulfonylurea derivative compounds were screened for their oral hypoglycemic activity in vivo using the alloxan-induced diabetic mouse model and proved more potent than either glibenclamide or oleanolic acid.

These and other features of the present disclosure will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a reaction scheme for the synthesis of sulfonylurea derivatives of oleanolic acid as described herein.

FIG. 2 is a graph illustrating the percentage change in blood glucose (BG) in diabetic mice after administration of glibenclamide, oleanolic acid, and compounds 3a and 3b (200 μg/kg body weight, acute study).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The sulfonylurea derivatives of oleanolic acid include compounds replacing the 5-chloro-2-methoxybenzoic acid moiety found in glibenclamide with oleanolic acid. The resulting triterpenoidal sulfonylurea derivatives are compounds having the following formula:

or a pharmaceutically acceptable salt thereof. The derivatives are synthesized by condensation of 3-oxo-Olean-12-en-28-oic acid with 4-(2-aminoethyl)benzenesulfonamide to form an intermediate product, followed by reaction with cyclohexyl isocyanate or 4-methylcyclohexyl isocyanate to give 3a or 3b. The sulfonylurea derivative compounds were screened for their oral hypoglycemic activity in vivo using the alloxan-induced diabetic mouse model and proved more potent than either glibenclamide or oleanolic acid. The sulfonylurea derivatives of oleanolic acid are therefore believed to be good candidates for the active ingredient of a pharmaceutical composition for oral administration in the treatment of diabetes.

The sulfonylurea derivatives of oleanolic acid will be better understood with reference to the following working examples, in which all melting points are uncorrected and were measured using an electrothermal capillary melting point apparatus. The IR spectra were recorded on a Shimadzu FT-IR 8101 PC infrared spectrophotometer. The ¹H-NMR spectra were determined with a Bruker AM-500 MHz spectrometer. The chemical shifts are expressed on the δ (ppm) scale using TMS (tetramethylsilane) as the internal reference standard. Mass spectra were recorded on a Finnigan SSQ operating at 70 eV. Elemental analysis was determined on a Perkin Elmer 240 (microanalysis) Microanalysis Center, Cairo University, Cairo, Egypt.

Example 1

Synthesis of Sulfonylurea Derivatives of Oleanolic Acid—General Reaction

An exemplary reaction scheme for preparing the sulfonylurea derivatives of oleanolic acid is shown in FIG. 1. Briefly, N-[(p-ethyl)-benzene-sulfonamide]-3-oxo-18β-olean-12-ene-28-carboxamide (2) is prepared by condensing 3-oxo-Olean-12-en-28-oic acid (1), also referred to a 3-oxo-oleanolic acid, with 4-(2-aminoethyl)benzenesulfonamide using the mixed anhydride technique adopted for the preparation of amides using trifluoroaceticanhydride. Compound 2 is then reacted with cyclohexyl isocyanate or 4-methylcyclohexyl isocyanate to produce the sulfonylurea derivatives 3a and 3b, respectively.

Example 2

Synthesis of Intermediate

In more detail, the intermediate compound, N-[(4-ethyl)-benzenesulfonamide]-3-oxo-18β-olean-12-ene-28-carboxamide (2), was synthesized as follows. Trifluoroaceticanhydride (4 mmol) was added dropwise to a solution of compound 1 (4 mmol) in dioxane (100 ml) at 0-5° C. The resulting mixture was reacted for 1.5 hr, then 4-(2-amino-ethyl)benzenesulfonamide (4 mmol) was added, and the resulting mixture was stored without stirring overnight. The reaction mixture was then evaporated under reduced pressure to dryness and the resulting solid product was crystallized from ethyl acetate/methanol to give compound 2. Yield 90%, mp. 287-289° C., [α]_D²⁵=+112 (c 1, CHCl₃); IR (KBr): 3551-3410 (NH₂, NH), 3050 (CH—Ar), 2931 (CH-aliph), 1748 (C═O), 1335 (S═O) cm⁻¹. ¹H NMR (pyridine-d₅): δ ppm 0.83 (d, 1H, CH), 0.89 (s, 3H, CH₃), 0.93 (s, 3H, CH₃), 0.98 (s, 3H, CH₃), 1.02 (d, 1H, CH), 1.06 (s, 3H, CH₃), 1.11 (s, 3H, CH₃), 1.18-1.27 (m, 8H, 2CH and 2CH₃), 1.37-1.70 (m, 7H, 7 CH), 1.73-1.75 (m, 2H, CH₂, C-2), 1.82-1.98 (m, 6H, 4CH and CH₂), 2.02-2.17 (m, 3H, 3CH), 3.37 (d, 1H, CH), 5.59 (s, 1H, CH), 6.71 (s, 1H, CONH) [olean skeleton], 2.62 (t, 2H, CH₂), 3.22 (t, 2H, CH₂), 5.13 (s, 1H, SONH), 6.14 (s, 1H, CONH), 7.15-7.28 (m, 4H, Ar). ¹³C NMR (pyridine-d₅): δ ppm 15.54, 16.56, 17.45, 18.64, 23.57, 23.61, 23.65, 26.67, 28.45, 28.48, 28.65, 31.45, 33.41, 33.54, 33.98, 34.68, 37.57, 39.43, 39.67, 39.85, 42.77, 42.83, 46.36, 46.69, 48.64, 55.45, 122.56, 144.74, 177.64, 210.65, (C1-C30) [olean skeleton], 32.24, 48.56 (ethylene bridge), 125.48, 127.23, 139.12, 145.34 (6C, Ar—C). MS (EI): m/z 637 (85%) [M+]. Anal. C₃₈H₅₆N₂O₄S (636.93): Found C, 71.60; H, 8.80; N, 4.35; S, 5.00; Calcd C, 71.66; H, 8.86; N, 4.40; S, 5.03.

Example 3

Synthesis of Final Product

In more detail, the final products, N₁-[4-(3-oxo-18β-olean-12-ene-28-amido-ethyl)benzenesulfonyl]-N₂-cyclohexylurea derivatives (3a,3b) were synthesized as follows. Unsubstituted or substituted cyclohexyl isocyanates, namely, cyclohexyl isocyanate or 4-methylcyclohexyl isocyanate (1.1 mmol), were added dropwise to a solution of compound 2 (1 mmol) in sodium hydroxide (8 ml, 10%) and acetone (20 ml) at 0-5° C. The resulting reaction mixture was kept at the same temperature for 3 hr, diluted with a water/methanol mixture (1:1), and then filtered off. The resulting filtrate was acidified with HCl, and a separated solid was filtered off, dried and recrystallized from acetic acid to yield sulfonylurea derivative compounds 3a or 3b, as follows.

N₁-[p-(4-Oxo-18β-olean-12-ene-28-amido-ethyl)-benzenesulfonyl]-N₂-cyclohexyl-urea (3a): Yield 81%, mp. 327° C., [α]_D²⁵=+123 (c 1, CHCl₃); IR (KBr): 3511-3386 (2NH), 3052 (CH—Ar), 2922 (CH-aliph), 1746 (C═O), 1698-1687 (N—C═O), 1335 (S═O) cm¹′. ¹H NMR (pyridine-d₅): δ ppm 0.84 (d, 1H, CH), 0.90 (s, 3H, CH₃), 0.95 (s, 3H, CH₃), 1.00 (s, 3H, CH₃), 1.04 (d, 1H, CH), 1.08 (s, 3H, CH₃), 1.15 (s, 3H, CH₃), 1.20-1.45 (m, 11H, 5CH and 2 CH₃), 1.50-1.58 (m, 3H, 3 CH), 1.75-1.95 (m, 7H, 3CH and 2 CH₂), 1.98-2.16 (m, 4H, 4 CH), 3.36 (d, 1H, CH), 3.44 (d, 1H, CH), 5.58 (s, 1H, CH), 6.70 (s, 1H, CONH) [Olean Skeleton], 1.11-1.13 (m, 5H, CH), 1.62-1.64 (m, 5H, CH), 3.18-3.20 (m, 1H, CH), 2.60 (t, 2H, CH₂), 3.20 (t, 2H, CH₂), 5.15 (s, 1H, SONH), 6.10 (s, 1H, CONH), 7.17-7.25 (m, 4H, Ar). ¹³C NMR (pyridine-d₅): δ ppm 15.69, 16.47, 17.76, 18.60, 23.51, 23.60, 23.67, 26.54, 28.45, 28.46, 28.85, 31.65, 33.46, 33.67, 33.74, 34.45, 37.56, 39.56, 39.58, 39.85, 42.77, 42.80, 46.36, 46.89, 48.44, 55.56, 144.79, 122.56, 177.45, 210.24 [30C, Olean Skeleton], 28.12, 34.40, 25.01, 25.39 [6C, cyclohexyl ring], 32.29, 48.70, (2C, CH₂CH₂), 166.70 (C═O), 125.40, 127.20, 139.10, 145.30 (6C, Ar—C). MS (EI): m/z 762 (100%) [M+]. Anal. C₄₅H₆₇N₃O₅S (762.09): Found C, 70.82; H, 8.80; N, 5.45; S, 4.16. Calcd C, 70.92; H, 8.86; N, 5.51; S, 4.21.

N₁-[4-(3-Oxo-18β-olean-12-ene-28-amido-ethyl)-benzenesulfonyl]-N₂-(4-methylcyclohexyl)-urea (3b): Yield 79%, mp. 200, [α]_D²⁵=+106 (c 1, CHCl₃); IR (KBr): 3523-3395 (2NH), 3048 (CH—Ar), 2932 (CH-aliph), 1747 (C═O), 1690-1680 (N—C═O), 1331 (S═O) cm⁻¹. ¹H NMR (pyridine-d₅): δ ppm 0.87 (d, 1H, CH), 0.91 (s, 3H, CH₃), 0.96 (s, 3H, CH₃), 1.02 (s, 3H, CH₃), 1.07 (d, 1H, CH), 1.10 (s, 3H, CH₃), 1.14 (s, 3H, CH₃), 1.22-1.46 (m, 11H, 5CH and 2 CH₃), 1.50-1.56 (m, 3H, 3CH), 1.67-1.89 (m, 5H, 3 CH and CH₂), 1.93-2.05 (m, 5H, 3 CH and CH₂), 2.12 (t, 1H, CH), 2.15-2.17 (m, 1H, CH), 3.30 (d, 1H, CH), 5.60 (s, 1H, CH), 6.75 (s, 1H, CONH) [Olean Skeleton], 0.78 (s, 3H, CH₃), 0.84 (m, 2H, CH), 1.12 (m, 1H, CH), 1.16-1.18 (m, 3H, 3 CH), 1.58-1.60 (m, 3H, 3 CH), 3.20-3.22 (m, 1H, CH), 2.68 (t, 2H, CH₂), 3.12 (t, 2H, CH₂), 5.13 (s, 1H, SONH), 6.10 (s, 1H, CONH), 7.18-7.28 (m, 4H, Ar). ¹³C NMR (pyridine-d₅): δ ppm 15.45, 16.90, 17.67, 18.45, 23.42, 23.45, 23.87, 26.89, 28.67, 28.78, 28.80, 31.56, 33.54, 33.65, 33.76, 34.76, 37.67, 39.45, 39.54, 39.67, 42.45, 42.65, 46.43, 46.56, 48.65, 55.43, 122.45, 144.65, 177.56, 210.65 [30C, Olean Skeleton], 22.7, 28.20, 33.10, 34.60, 36.40 [6C, cyclohexyl ring], 32.56, 48.77 (2C, CH₂CH₂), 166.78 (C═O), 125.47, 127.26, 139.11, 145.38 (6C, Ar—C). MS (EI): m/z 776 (100%) [M+]. Anal. C₄₆H₆₉N₃O₅S (776.12): Found C, 71.19; H, 8.96; N, 5.41; S, 4.13. Calcd C, 71.10; H, 8.90; N, 5.35; S, 4.10.

Example 4

Evaluation of In Vivo Oral Hypoglycemic Activity

The sulfonylurea derivatives of oleanolic acid were screened for their oral hypoglycemic activity in vivo using the alloxan-induced diabetic mouse model. In an acute evaluation, the percentage change in blood glucose levels in diabetic mice after oral administration of the test compounds (200 μg/kg body weight) was measured and summarized in Table 1 and FIG. 2.

Briefly, animals were fasted overnight and the fasting blood glucose (BG) (0 hour) levels were calculated. Test and control compounds were administered at a fixed dose of 200 μg/kg body weight orally (homogenized suspension in 0.5% carboxymethyl cellulose (CMC) and permissible amounts of Tween 80). Animals in the vehicle-treated group were given an equal volume of 0.5% CMC and control group animals were untreated. Blood samples were removed from all animals at 2, 4, 6 and 24 hours and the percentage change in BG was calculated. The data were analyzed by one-way ANOVA followed by Dunnett's test. The results were expressed as mean±standard error of mean for each group, n=6 for each group, and p<0.01 or p<0.05 was considered as statistically significant. As illustrated in Table 1 and FIG. 1, the sulfonylurea derivative compounds showed a more potent anti-diabetic activity and a longer duration of action than the reference anti-diabetic drugs, glibenclamide and oleanolic acid.

The sulfonylurea derivative compounds were also screened for their oral hypoglycemic activity after several days of administration using the alloxan-induced diabetic mouse model, and percentage changes in blood glucose levels after oral administration (200 g/kg body weight) were recorded (Table 2).

Briefly, animals were fasted overnight, and the fasting BG (0 day) levels were calculated. Test and control compounds were administered orally for 21 days at a fixed time and a fixed dose of 200 μg/kg body weight (homogenized suspension in 0.5% CMC and permissible amounts of Tween 80). After 21 days, treatment was stopped and animals were rested for a period of 7 days. Animals in the vehicle-treated group were then given an equal amount of 0.5% CMC and those of control group were untreated. Blood samples were removed from all animals throughout the course of the study at 7, 14, 21 and 28 days, and percentage change in BG was calculated. The data were analyzed by one-way ANOVA, followed by Dunnett's test. The results were expressed as mean±standard error of mean for each group, n=6 for each group, and p<0.01 or p<0.05 was considered as statistically significant (Table 2). The sulfonylurea derivative compounds showed several times more potent anti-diabetic activity than the reference anti-diabetic drugs, glibenclamide and oleanolic acid.

It is to be understood that the oleanolic acid sulfonylurea as an anti-diabetic is not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.