IE47490B1 - 4-desacetoxy-oxo-indole-dihydroindole intermediates - Google Patents

Description

The invention relates to novel 4-desacetoxy-4-oxoindole-dihydroindoles useful as intermediates in the preparation of 4-desacetoxy-4a~hydroxyindole-dihydroindole antimitotic agents.

The Vinca alkaloids, a group of dimeric indoledihydroindoles, have achieved considerable prominence as marketed or experimental chemotherapeutic drugs for the treatment of susceptible carcinomas, sarcomas, and leukemias. These agents are used both alone and in com10 bination with other oncolytic agents. As a class, the Vinca alkaloids include compounds obtainable from the leaves of Vinca rosea, derivatives produced by chemical modification thereof and more recently, dimeric alkaloids produced by coupling two monomeric indoles via a modified Polonovski reaction-see Langlois and Potier, Tetrahedron Letters, 1099 (1976), Potier, et al., J.C.S. Chem. Comm., 670 (1975), Kutney et al., Heterocycles, 3, 205 (1975) and Atta-ur-Rahman, Tetrahedron Letters, 2351 (1976) .

A majority of the known Vinca alkaloids can be represented by the following formula: In the above formula, where R is acetoxy, 3 4 5 R is methyl, R is hydroxyl, R is ethyl and R is H, vinblastine is represented; where R1 is acetoxy, 3 4 5 R is formyl, R is hydroxyl, R is ethyl and R is H, vincristine is represented; where R is acetoxy, 3 4 5 .

R is methyl, R is ethyl, R is hydroxyl and R is H, leurosidine is represented; where R3 is acetoxy, R2 is methyl, R3 and R3 are H and R4 is ethyl, deoxy 12 5 VLB A is represented; where R , R and R are the same as in deoxy VLB A (4'-deoxyvinblastine) but R3 is ethyl and R4 is hydrogen, deoxy VLB B (4'— deoxyleurosidine) is represented; where R3 is 3 4 5 acetoxy, R is methyl, R is ethyl and R and R taken together form an α-epoxide ring, leurosine is 13 4 5 represented; and where R , R , R and R are the 2 same as in leurosine but R is formyl, leuroformine (N-formylleurosine) is represented.

The above-mentioned alkaloids are described in the following publications; leurosine (vinleurosine— U.S. Patent No. 3,370,057), VLB (vincaleukoblastine, vinblastine—U.S. Patent No. 3,097,137), leurosidine (vinrosidine) and vincristine (leurocristine or VCR) (both in U.S. Patent No. 3,205,220), and deoxy VLB A and Β, Tetrahedron Letters, 783 (1958). Other alkaloids obtainable from vinca rosea include 4desacetoxy vinblastine (U.S. Patent 3,954,773); 4-desacetoxy-3'-hydroxyvinblastine (U.S. Patent 3,944,554); leurocolombine (2'-hydroxy VLB—U.S.

Patent No. 3,890,325) and vincadioline (3'-hydroxy VLB—U.S. Patent 3,887,565).

Two of the above alkaloids, VLB and vincristine, are now marketed as drugs for the treatment of malignancies, particularly the leukemias and related diseases in humans. Of these marketed >* compounds, vincristine is a most active and useful agent in the treatment of leukemias but is also the least abundant of the antineoplastic alkaloids of Vinca rosea. Jovanovics et al.—U.S. Patent No. 3,899,493--have developed an elegant oxidative procedure for converting the more abundant alkaloid VLB to vincristine employing chromic acid in acetone and acetic acid at about -60°C. The same procedure has been used to prepare leuroformine (N-formyl10 leurosine) from leurosine—see Belgian patent No. 811,110. Leuroformine is currently undergoing a clinical trial in Europe, chiefly in treatment of the leukemias and of multiple myeloma.

Chemical modification of VLB and vincristine has included hydrolysis of the 4-acetoxy group to yield 4-desacetyl VLB (DAVLB) or 4-desacetylvincristine (DAVCR) followed by reesterification with other acyl and amino-acyl groups—see U.S. Patents Nos. 3,392,173 and 3,387,001—, and replacement of the C-3 ester function by an amide function--see Belgian patent 837,390. One of the former 4-acyl derivatives, the 4-N,N-dimethylglycine ester underwent a brief clinical trial and one of the latter, vindesine, (4-desacetyl VLB C-3 carboxamide) is currently being tested clinically against a variety of neoplasms.

Other chemical modification of the VLB molecule such as hydrolysis and decarboxylation of the C-18* carbomethoxy group has resulted in a loss of anti-cancer activity as has the formation of >* N-oxides; i.e., pleurosine (leurosine N-oxide). Oxidative attack on VLB under temperatures higher than -60°C. or in neutral or basic solution has resulted in the formation of a chemotherapeutically inactive compound, vinamidine, represented by the following formula: s' CHO CsHs I ι ο]:,· ,r \ /\6/ \1Z ' V1S V \<«c-o-ch3 14 , I „ CHsO” I I . I,, I s· ch3 iiVYV.....~z ^0H CHs O-CO-CH3 CHa II C-0-CH3 II Oxidation of VLB with MnO., in acetone or CH^Cl^ at ambient temperature has also yielded vinamidine. The same alkaloid has been encountered in alkaloidal fractions from Vinca rosea leaves— see Tafur et al. J. Pharm. Sci., 64, 1953 (1975)— but the structure assigned therein (IX on page 1956) is now believed to be incorrect and the above structure more closely represents the NMR, IR, and mass spectral data obtained from physiochemical studies of the compound. Vinamidine may arise from oxidative attack on VLB in which a vincinal 4',5'dihydroxy-derivative is formed which glycol, upon further oxidation, splits between the hydroxyls(4',5'bond) to yield a ring-opened derivative such as II above. 4-Desacetyl VLB and other 4-desacetyl compounds; i.e., those in which in Formula I is hydroxyl, are not oxidized to the corresponding 4-oxo derivative by the Jovanovics low-temperature chromic acid oxidation (see Cullinan - Ser. No. 723,350). Theoretical considerations emphasize the difficulty of oxidizing the secondary hydroxyl at C-4 to a carbonyl. The ring containing the C-4 carbon is locked into position since four of the ring carbons are fused into other rings of the vindoline portion of the molecule. In order to undergo oxidation from a secondary hydroxyl to a carbonyl, the bond angles of the C-4 carbon would have to change from the tetrahedral angle (108°) to the sp angle (120°). Such a change in the fused ring environment in which the C-4 carbon finds itself would involve considerable ring strain.

It is an object-, of this invention to prepare 4-oxo-derivatives useful in the preparation of 4v compounds of oncolytically active Vinca alkaloids having either a different anti-tumor 1C spectrum, or lessened or different side effects, or both as compared with the marketed drugs, vinblastine and vincristine.

In fulfillment of the above and other objects, this invention provides an indole-dihydroindole of the formula r3 ΛΓ Γ'Ί^,Γ \^C-O-CHa 14 , 1.. wherein: CHaOθ/'\ I“f ii ,Z\ \·Λζ w C-R II •CHs .

R IS CH, or CHO; J 5 1 when taken singly, R is H and one of R 4749ο and R is OH or H and the other is C2H^ and 4 5 when R and R are taken together, they 3 form an α-epoxide ring and R is C^H , and 6 7 R and R taken together are =0; R is OCHj or NH-NHj; and pharmaceutically acceptable acid addition salts thereof.

These compounds are useful in the preparation of the 4a-hydroxy~ and 4ct-acetoxy-compounds described in our copending Patent Application No. 47489 ( that is compounds fi 7 11 2_0 in which R is H and R' is OR , R being H or acetyl) , which have antimitotic properties. Their conversion to the active compounds is described in that patent application.

The compounds of the invention are prepared by reacting an indole-dihydroindole of the above formula wherein R, R3, R2, R3, R4 and R3 are as above and wherein R8 is OH and R is H with an oxidizing agent in a liquid phase.

Also included within the scope of this invention are the pharmaceutically-acceptable acid addition salts of the above alkaloidal bases including salts derived from inorganic acids such as: hydrochloric acid, nitric acid,phosphoric acid, sulfuric acid, hydrobromic acid, hydriodic acid, nitrous acid, phosphorus acid and the like, as well as salts of organic acids including aliphatic mono and dicarboxylic acids, phenyl-substituted alkanoic acids, hydroxy alkanoic and alkandioic acids, aromatic acids, aliphatic and aromatic sulfonic acids, etc. Such pharmaceutically-acceptable salts thus include the sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, acetate, propionate, decanoate, caprylate, acrylate, formate, isobutyrate, caprate, heptanoate, propiolate, oxalate, malonate, succinate, suberate, sebacate, fumarate, maleate, benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate, hydroxybenzoate, methoxybenzoate, phthalate, terephthalate, benzenesulfonate, toluenesulfonate, ohlorobenzenesulfonate, xylenesulfonate, phenylacetate, phenylpropionate, phenylbutyrate, citrate, lactate, 2-hydroxybutyrate, glycollate, malate, tartrate, methanesulfonate, propanesulfonate, naphthalene-l-sulfonate, napthalene2-sulfonate and the like salts.

The 4-oxo indole-dihydroindole compounds of Formula V are prepared by oxidizing a 4&-hydroxy compound wherein Rg is OH, R? is H and R is OCH, with Moffat's Reagent - dimethyl-sulfoxide (DMSO), dicyclohexylcarbodiimide (DCC) and ortho phosphoric acid or other similar oxidizing agents. This reagent was originated by Pfitzner and Moffat, J. Am. Chem. Soc., 85, 3027 (1963) 87 5661, 5670 (1965) - see also Fieser and Fieser, Reagents for Organic Synthesis, 1, 304, 2 162 (John Wiley and Sons, Inc., 1967).

In carrying out the synthesis of the 4-oxo compounds of this invention with Moffat’s reagent a 40-hydroxy compound of Formula V, R® is OH (as the free base) and the dicyclohexylcarbodiimide are dissolved in DMSO 'at room temperature and the phosphoric acid is then added. The reaction mixture is agitated until solution is complete (5-10 minutes). The reaction flask is then stoppered and allowed to remain at room temperature until the reaction is substantially complete — 5 to 6 hours—as shown by TLC analysis of aliquot samples worked up by standard procedures. The desired product is isolated by diluting the reaction product with dilute sulfuric acid, filtering the resulting mixture and washing the precipitated dicyclohexylurea with 1 percent aqueous sulfuric acid. The filtrate is made basic with 14 N aqueous ammonium hydroxide and extracted into a water immiscible organic solvent such as methylene dichloride or ether. The organic extracts are combined, dried, and the solvent removed by evaporation. The residue containing the desired 4-oxo compound is purified by chromatography, gradient elution chromatography, or gradient pH extraction.

The latter procedure is preferred.

In carrying out the above-mentioned oxidation employing Moffat's Reagent, it is customary to use an excess of the reagent. For example, an a* excess of dicyclohexylcarbodiimide of 2-10 fold and a 2 to 5 fold excess of ortho phosphoric acid are employed, Dimethylsulfoxide is used as both a reactant and a solvent and it is therefore, always in a 10 to 20 fold excess. It is preferred to employ a 6-7 molar excess of dicyclohexylcarbodiimide and a 2.5 to 3 molar excess of ortho phosphoric acid per mole of starting material. The reaction can be carried out at temperatures ranging from 20°C. to 50°C. , but it is preferred to employ temperature of about 20°C. As would be expected, the higher the temperature, the faster the reaction. However-, temperatures in excess of about 25°C. may give rise to excessive quantities of decomposition products. On the other hand, the reaction does not go rapidly to completion at 20°C. and time periods of from 5 to 7 hours are needed for substantial completion of the oxidation procedure. Longer periods of time will, of course, be necessary if lower reaction temperatures are employed.

An alternative oxidizing agent is the combination of N-chlorosuccinimide and dimethylsulfide, used in conjunction with a tertiary amine such as triethylamine. Other equally useful oxidizing agents will readily suggest themselves to these skilled in the art.

Compounds according to Formula V wherein R 2 is OCHg, Rg and R? art? =0, and R is CHO can be prepared by low temperature oxidation of the corre2 sponding compound wherein R is CHg by the procedure of Jovanovics et al., U.S. patent 3,899,493. 4749 0 The starting materials useful to prepare the 4-oxo compounds of this invention - those materials represented by Formula V wherein R is OCH^, Rg is OH and R? is H- are prepared by hydrolysis of the corresponding C-4 acetates. The compounds according 2 to Formula V in which R is CH^ and Rg is acetoxy and R? is H are known compounds; i.e., vinblastine is disclosed in U.S. Patent 3,097,137, leurosidine in U.S. Patent 3,205,220, leurosine, in U.S. Patent 3,370,057 and deoxy VLB A and B in Tetrahedron Letters, 783 (1958). The corresponding compounds in 2 which R is CHO are also known and include vincristine, also disclosed in U.S. Patent 3,205,220, leuroformine, Belgian patent 811,110, 4'-deoxyvincristine and 4' - deoxy - 1 - formylleurosidine in U.S. Patent 4, 143, 041. The remaining compound, 1 - desmethyl - 1 - fornylleurosidine is prepared by the low temperature oxidation of leurosidine with chromic oxide according to the procedure of U.S. patent 3,899,493. The corresponding 4-desacetyl compounds are prepared from the above vinca alkaloids by hydrolysis either under acidic or basic conditions. Hargrove, Lloydia, 27, 340, (1964) first prepared 4-desacetyl vinblastine by the acidic hydrolysis of vinblastine using large volumes of absolute methanol saturated at 0°C. with anhydrous hydrogen chloride.

A contact time of about 6 hours was used. Acidic hydrolysis also seems to be the procedure of choice for preparing 4-desacetyl deoxy VLB B and A.

·# However, it has been found that an alkaline hydrolysis procedure is preferred for the preparation of 4-desacetyl derivatives of both leurosine and vinblastine. According to this procedure, sodium carbonate in refluxing methanol is employed as the hydrolytic medium.

This invention is further illustrated by the following specific examples.

Example 1 4-Desacetoxy-4-oxovinblastine A reaction mixture was prepared by adding 3.0739 g. of 4-desacstoxy-4i-hydroxy vinblastine and 5.8929 g. of dicyclohexy^carbodiimide to 20 ml. of DMSO. 1.2185 Grams of ortho phosphoric acid (anhydrous) dissolved in 5 ml. DMSO were added. The reaction flask was stoppered and swirled until solution was complete.

The reaction mixture was maintained at ambient temperature (18-22°C.) for 5 hours, and was then poured into a mixture of ice and 1% aqueous sulfuric acid. The precipitated dicyclohexylurea was removed by filtration and the filter cake washed with 1% aqueous sulfuric acid. The aqueous layer was made basic with 14 N aqueous ammonium hydroxide. This aqueous alkaline mixture was extracted several times with methylene dichloride. The methylene dichloride extracts were combined and dried and the solvent removed therefrom by evaporation in vacuo leaving a residue containing 4-desacetoxy-4-oxovinblastine (2.6534 g.). The residue was dissolved in 1% aqueous sulfuric acid, the resulting solution filtered, and the filtrate made basic with 14 N NH.OH as before.

Extraction with CHjClj followed by drying and removal of the solvent yielded a residue. Thin-layer chromatography of an aliquot over silica gel using a 1:1 ethyl acetate/ethanol solvent mixture showed the residue to consist of essentially one-spot material. The residue was combined with 298 mg. of a similar residue from a chromatographic separation procedure in a previous run, and the combined material dis47490 ί solved in 400 ml. of a 0.1 M citric acid buffer, (pH = 2.35) and subjected to a gradient pH extraction procedure. The acidic solution was extracted with 400 ml. of benzene and the pH adjusted to 3.0. The solution was again extracted with 400 ml. of benzene, the pH raised again, etc. The following chart gives the pH of the solution in column 1 and in column 2, the weight of material in the fraction after removal of the benzene. Each fraction was analyzed by thin-layer chromatography as before for the presence of 4-desacetoxy-4-oxovinblastine.

Table 1 pH of weight in mg. aqueous of extracted layer product 2.35 205.8 (discarded) 3.0 167.1 3.5 270.6 4.0 6 71 · 4 ί f ,. j \ f- (combined) 4.5 740.lj 5.0 257.7 5.5 123.0 6.0 66.7 6.5 26.7’ 7.0 23.8 7.5 12.8 - (discarded) 8.0 22.7 9.0 17.8/ Fractions taken at pH 3.0-5.0 were combined with a filtrate from a crystallization of 4-desacetoxy4-oxovinblastine obtained previously by chromato47490 graphy, and the combined fractions dissolved in 400 ml. of 0.1 m citric acid buffer as before. A second gradient pH extraction procedure was carried out as above except that, in some instances, more than one extraction with a 400 ml. portion of benzene was carried out. Table 2 gives the results of this extraction procedure. Column 1 gives the pH of the aqueous layer, Column 2 the number of extractions with 400 ml. portions of benzene, and Column 3, the weight in milligrams of extracted product after evaporation of the solvent.

Table 2 pH of aqueous layer 2. 35 2.75 3.15 3.55 4.00 4.5 .0 .5 6.0 8.0 no. of extractions weight in mg. of extracted product 252.4 (discarded) 97.1 114.2 276.1 1154.2 213.2 89.7 32.2 18.7 13.5 The fraction at pH = 4.0 weighing 1.1542 g. was crystallized from a methanol/water mixture. 854.3 Milligrams of crystalline 4-desacetoxy4-oxovinblastine were obtained. Infrared and NMR spectra were in accordance with the proposed structure. 490 Alternate Preparation of 4-Desacetoxy-4-oxovinblastine A solution was prepared containing 2.47 g. of 4-desacetoxy-4ii-hydroxy vinblastine in 37 ml. of toluene and 7.4 ml. of methylene dichloride. 1.29 Grams of N-chlorosuccinimide were suspended in 30 ml. of anhydrous toluene and the suspension stirred under a nitrogen atmosphere with cooling. 1.06 Milliliters (0.9 g.) of dimethylsulfide were added to this suspension in dropwise fashion. The mixture was then stirred for an additional 15 minutes. Next, the solution of the 4-desacetylvinblastine was added in dropwise fashion over a period of 5 minutes at 0°C. to the mixture of N-chlorosuccinimide and dimethylsulfide in toluene. (The following volumes of solvents were used: 15 times weight of starting material for toluene on a weight/volume basis, 3 times -weight of starting material on a weight/volume basis of starting material for N-chlorosuccinimide and an excess of dimethylsulfide. After stirring for 5.6 hours at 0°C., 2.02 ml. (1.47 g.) of triethylamine were added and the reaction mixture was stirred for an additional one-half hour at room temperature and then stored overnight in the refrigerator. Thin-layer chromatography indicated that all of the starting material, 4-desacetylvinblastine, had been consumed, and that the reaction mixture consisted essentially of single spot material. The reaction mixture was diluted with ether plus methylene dichloride and the resulting organic layer washed three times with water and then dried. Removal of the solvents in vacuo yielded a yellow solid comprising 4-desacetoxy-4-oxovinblastine; weight = 2.39 g- This material was chromatographed over 240 g. of activity I silica. The chromatogram was developed with 400 ml. portions of 1:1 methylene dichloride/ethyl agetate containing 9, 13.5, 20, 30, and 45 percent added methanol. After 700 ml. of eluent had been collected, 20 ml. fractions were then taken. Fractions 21-45 yielded, when combined and the solvents evaporated, 1.28 g. of a tan solid, 4-desacetoxy-4-oxovinblastine. 4-Oxo-4-desacetoxyleurosidine, 4-oxo4-desacetoxyvincristine, 4-oxo-4-desacetoxy-ldesmethyl-l-formylleurosidine, 4-oxo-4-desacetoxyleurosine, 4-oxo-4-desacetoxy-l-leuroformine, 4oxo-4-desacetoxy-4'-deoxy VLB, 4-oxo-4-desacetoxy41-deoxyleurosidine and the corresponding 1formyl derivatives are prepared in similar fashion by oxidizing the corresponding 4-desacetyl compound with Moffat's Reagent or similar oxidizing agent.

Leurosidine, deoxy VL3 A, deoxy VLB B and leurosine can be subjected tc the same series of reactions; i.e., mild alkaline hydrolysis to form the 4-desacetyl derivative and oxidation of the 4-hydroxy derivative to the.4-oxo derivative.

Claims (13)

1. CLAIMS wherein: 5 R 2 is CH or CHO; J 5 3 when taken singly, R is H and one of R and R is OH or H and the other is C-H4 5 5 and when R and R are taken together, they form an α-epoxide ring and R 3 is A· 6 7 and R and R taken together are = 0; and R is 0CH 3 or NH-NH 2 ; and pharmaceutically acceptable acid addition salts thereof. 2. 3

2. A compound according to claim 1 wherein R , R , 5 R 4 , R 2 , R 2 and R 7 are as defined in claim 1 and R is OCH 3 .

3. 4-Desacetoxy-4-oxo-vinblastine.

4. A process for preparing a compound according to claim 1 which comprises reacting an indoledihydroindole of formula V wherein R, R^, R 2 , R 2 , R 4 and R^ are as defined in claim 1 6 7 10 and wherein R is OH and R is H with an oxidizing agent in a liquid phase.

5. A process according to claim 4 for preparing 4desacetoxy-4-oxoindoledihydroindole wherein the oxidizing agent is dicyclohexyl carbodiimide, o-phosphoric acid and 15 dimethylsulfoxide.

6. A process according to claim 4 for preparing 4desacetoxy-4-oxo-indoledihydroindole wherein the oxidizing agent is N-chlorosuccinimide and dimethylsulfide in conjunction with a tertiary amine. 20

7. A process according to either of claims 4 and 5 for preparing 4-desacetoxy-4-oxo-indoledihydroindole wherein the 4-desacetyl-4B-hydroxy-indole-dihydroindole is reacted with dicyclohexyl carbodiimide, o-phosphoric acid and dimethyl47490 sulfoxide at 18-22° for 5 hours.

8. A process according to either of claims 4 and 6 for preparing 4-desacetoxy-4-oxoindole-dihydroindole wherein the 4-desacetyl-48-hydroxy-indole-dihydroindole is reacted with5 N-chlorosuccinimide and dimethylsulfide in conjunction with a tertiary amine in toluene under nitrogen atmosphere with stirring for 6 hours at 0°C.

9. A process according to any of claims 4, 5 and 7 for preparing 4-desacetoxy-4-oxo-vinblastine wherein 4-desacetyl 10. 4£-hydroxy vinblastine is reacted with dicyclohexylcarbodiimide, o-phosphoric acid and dimethyl sulfoxide at 18° to 22°C. for 5 hours.

10. A process according to any of claims 4, 6 and 8 for preparing 4-desacetoxy-4-oxo-vinblastine wherein 4-desacetyl· 15 46-hydroxyvinblastine is reacted with N-chlorosuccinimide and dimethylsulfide in conjunction with a tertiary amine in toluene under nitrogen atmosphere with stirring for 6 hours at 0°C.

11. A compound according to claim 1 substantially as des20 cribed in either of Examples 1 and 2.

12. A compound according to claim 1 when prepared by a process according to claim 4.

13. A process according to claim 4 substantially as described in either of Examples 1 and 2.