|Title of Invention||
"PROCESS FOR SYNTHESIZING DISULFIDES"
|Abstract||A process for preparing disodium 2,2'-dithiobis ethane sulfonate, which comprises: (a) brominating sodium isethionate in aqueous solution by addition of hydrobromic acid, in the absence of isethionic acid, to form sodium 2-bromoethane sulfonate as a first intermediate; (b) reacting the first intermediate with sodium thioacetate to form sodium 2- acetylthioethane sulfonate as a second intermediate; (c) reacting the second intermediate with a strong base to form sodium 2- mercaptoethane sulfonate as a third intermediate; (d) oxidizing the third intermediate with oxygen at a temperature of 30°C to form disodium 2,2'-dithiobis ethane sulfonate; and (e) isolating the disodium 2,2' -dithiobis ethane sulfonate.|
|Full Text||The present invention relates to a process for preparing disodium 2,2'-dithiobis ethane sulfonate.
BACKGROUND OF THE INVENTION
 This invention relates to a chemical synthetic process and will have application to a process for synthesizing disulfide compounds and intermediates thereof.
 Mesna (sodium 2-mercaptoethane sulfonate; Mesnex®; Uromitexan®) and dimesna (disodium 2,2'-dithiobis ethane sulfonate; BNP7787; Tavocept™) are known therapeutic compounds that have heretofore demonstrated a wide variety of therapeutic uses. Both mesna and dimesna have been shown to be effective protective agents against certain specific types of toxicity associated with the administration of cytotoxic drugs used to treat patients for various types of cancer.
 In particular, mesna is an approved agent in most major markets, and has been used with some success in mitigating the toxic effects of cytotoxic agents such as ifosfamide, oxazaphosphorine, melphalane, cyclophosphamide, trofosfamide, sulfosfamide, chlorambucil, busulfan, triethylene thiophosphamide, triaziquone,.and others, as disclosed in U.S. Patent 4,220,660, issued September 2,1980..
 Dimesna is in late stage human clinical trials in most major pharmaceutical markets, and has exhibited efficacy in mitigating the undesired toxic effects of various platinum antineoplastic agents, as well as the neurotoxic effects of paclitaxel.
 Further, pharmacological profiles of each compound indicate that, if proper conditions are maintained, mesna and dimesna do not prematurely inactivate primary therapeutic drugs to a significant degree. Thus, neither compound is likely to significantly reduce activity of the chemotherapeutic ageat, and in many cases, dimesna has been observed to potentiate the effect of the main drug on targeted cancer cells.
 The structures of both mesna and dimesna are shown below:
 As is well known, dimesna is an oxidative dimer of mesna. In the slightly basic
(pH ~ 7,3), oxygen rich environment found in blood plasma, dimesna is present in large part in its
oxidized form. In mildly acidic, low oxygen conditions, in the presence of a reducing agent such as
glutathione reductase, conditions prevalent in the kidneys, dimesna is reduced to mesna.
 Mesna acts as a protective agent for a number of cytotoxic agents by converting a toxic
metabolite of the cytotoxic agent (acrolein in the Case of ifosfamide) to a relatively harmless
compound in vivo. This action is particularly evidenced hi the coadministration of mesna and an
oxazaphosphorine. Dimesna acts as a protective agent by converting a toxic hydroxy or aquo
moiety of the active agent to a relatively harmless mercaptan, particularly in the administration of
dimesna along with a platinum agent.
 Mesna and dimesna, as well as some analogues of these compounds, have excellent
toxicity profiles in mammalian species. Dimesna has been administered intravenously to mice and
dogs in doses higher than the accepted oral LD50 for common table salt (3750 mg/kg), with no
 Mesna, and other analogues with free thiol moieties, constitute the more physiologically
active form of the two types of compounds described in this specification. These compounds
manifest their activity by providing free thiol moieties for terminal substitution at locations where a
terminal leaving group of appropriate configuration is located.
 Dimesna and other disulfides can be activated intrapellularly by glutathione reductase, a
ubiquitous enzyme, thereby generating high" concentrations of intracellular free thiols; These free
thiols act to scavenge the free radicals and other nucleophilic compounds often responsible for
causing cell damage.
 This profile is especially significant in explaining the success of dimesna in controlling
and mitigating the toxic effects of platinum complex antitumor drugs. The mechanism for action in
the case of cisplatin (cis-diammine dichloro platinum) is explained in United States Patent
5,789,000, the disclosure of which is incorporated herein by reference.
 Mesna, dimesna, and analogues of these compounds have been the subject of several
prior pharmaceutical uses described in the literature and in prior patents, both in the United States
and around the world.
 Mesna, dimesna, and analogues thereof have been previously synthesized from
commonly available starting materials, using acceptable routes well known in the art. See, for
example, United States Patents 5,808,140. One such method involves the two-step, single pot
synthetic process for making dimesna, and other sulfur-containing alkali metal compounds of the following Formula I:
 R1 is hydrogen, -X-lower alkyl or -X-lower alkyl-R3;
 R2 is -lower alkyl-R4;
 R3 and R4 are each individually-S03M or-PO3M2;
 X is absent or is sulfur; and
 M is an alkali metal.
 The prior process involves a two-step single pot synthetic process, which results in the conversion of an alkenyl sulfonate salt or acid to the desired Formula I compound. The process in the case of rhesna is a single step process that converts the alkenyl sulfonate salt to mesna or a mesna derivative by reacting with an alkali metal sulfide or with hydrogen sulfide.  If the desired end product is dimesna or a dimesna analogue, a two-step single pot process is involved. Step 1 is as described above. Step 2 of the process is performed in the same reaction vessel as Step 1 without the need to purify or isolate the mesna formed during that step. Step 2 includes the introduction of oxygen gas into the vessel, along with an increase in pressure and temperature above ambient values, at least 20 pounds per square inch (psi) and at least 60°C. Dimesna or a derivative thereof is formed in essentially quantitative yield.  Hitherto, it is known that disodium 2,2'-dithiobis ethane sulfonate is produced, for example, by oxidizing sodium 2-mercaptoethane sulfonate, which is obtained by addition to sodium vinyl sulfonate, with oxygen at 60°C. However, this process has a problem, in that it produces a byproduct, disodium 2,2'-monothiobis ethane sulfonate, that is difficult to remove.  A method is also known for producing disodium 2,2'-dithiobis ethane sulfonate which comprises allowing sodium 2-bromoethane sulfonate to react with sodium thioacetate, neutralizing the product to give sodium 2-mercaptoethane sulfonate and oxidizing it with oxygen to afford disodium 2,2'-dithiobis ethane sulfonate (U.S. Published Patent Application Publication No. US 2004/0024346 Al, published February 5,2004). In this method, several unknown by-products are formed at 50-60°C, recommended as the oxidizing temperature, and it is difficult to remove them. Further, solids tend to be produced while drying, because the solvent for crystallizing is a mixture of ethanol with water.
 The raw material, sodium 2-bromoethane sulfonate, is known to be prepared by allowing a 1:1.9 mixture of isethionic acid with sodium isethionate to react with hydrobromic acid, cooling the product to give crystals and recrystallizing from 96% ethanol (German Democratic Republic Patent No. DD 154,815). However, isethionic acid is expensive.
 Therefore, there is a need for and it is desired to establish a method for producing disodium 2,2'-dithiobis ethane sulfonate from available raw compounds in good yield with high purity. The present invention satisfies this need.
BRIEF SUMMARY OF THE INVENTION
 This invention relates to a novel and economical process for synthesis of dimesna or a related disulfide compound of Formula II:
 R5 is -lower alkyl or -lower alkyl-R6;
 R2 is -lower alkyl-R4;
 R4 and R6 are each individually -SO3M, -PO3M2 or -CO2M; and
 M is an alkali metal.
 This process is carried out in an aqueous solution in one pot or one vessel, and includes an initial step of halogenating a starting material having a Formula III:
 Y is a displaceable group displaceable by a S^2 nucleophilic substitution reaction;
to form a first intermediate having a Formula (IV):
 A is a halogen;
 which is reacted with an alkali metal mecaptan having a base-sensitive labile protective
group to form a second intermediate having a Formula (V):
 Z is a base-sensitive labile protective group;
 which is reacted with a strong base to form a third intermediate having a Formula (VI):
. , R2-SH; (VI)
 which is then oxidized to form the disulfide compound of Formula n, which is then
 An object of this invention is to provide for a novel process for synthesizing reducible
disulfides. Preferably, the disulfides, such as dim«sna, are pharmaceutically active.
DETAILED DESCRIPTION OF THE INVENTION
 The preferred embodiments herein described are not intended to be exhaustive or to limit the invention to the precise form disclosed. They have been chosen and described to explain the principles of the invention, and its application and practical use to thereby enable others skilled in the art to follow and apply its teachings.  Definitions
 "About5' as used herein means plus or minus ten percent (i; 10%) of the value to which the term "about" relates.
 "Halogen" and related terms such as halogenating, halo, haloacid, as used herein means chlorine, bromine or iodine, but not fluorine, and such related terms refer to these halogens but not fluorine.
 "Lower alkyl" as used herein means a straight chain alkyl group of 1 to 4 carbon atoms.  "Percent" or "%" as used herein means percent by weight of the overall composition containing the compound or other component with which percent or % is used, except with reference to the definition of "about" set forth above, where percent or % merely refers to any value to which "about" relates.
 "Substantially pure" as used herein means at least 90% pure, preferably at least 95% pure, and more preferably at least 99% pure.
 The present invention is a process for making compounds of Formula II:
 R5 is -lower alkyl or -lower alkyl-R6;
 R2 is -lower alkyl-R4;
 R4 and R6 are each individually -SO3M, -P03M2 or -CO2M; and
 M is an alkali metal; and
 wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl; R5 is
preferably -lower alkyl-R6; preferably each of R4 and R6 is -SOsM or -PO3M2; and more preferably
each of R4 and R6 is-SOaM; and M is preferably Na.
 This process is a one-pot process carried out in an aqueous solution, and includes the
steps set forth above in the Summary, to form a substantially pure disulfide compound of Formula II
in good yield, especially for a one-pot process.
 More particularly, the process for synthesizing a substantially pure disulfide compound
of Formula II comprises the steps of:
 (a) Halogenating, and preferably brominating, by reacting, preferably with mixing at a
rate of about 15 to about 150 rpm, about 1 to about 10 mol equivalents, preferably about 1 to about 5
mol equivalents of ahaloacid, preferably HBr, in aqueous solution with about 1 mol equivalent of a
starting material of Formula III:
 Y is a displaceable group displaceable by a S*t2 nucleophilic substitution reaction;
and wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl; preferably R4 is -SOsM or -POslVk; and more preferably R4 is -SOsM; and M is preferably Na; and the displaceable group may be any suitable displaceable group, such as, without limitation, hydroxyl, mesyl or tosyl, with hydroxyl being preferred. The preferred starting materials include any alkali isethionate salt, such as sodium isethionate or potassium isethionate, and preferably is sodium isethionate. Upon completion of the reaction a first intermediate of Formula IV is obtained and isolated:
 A is a halogen; and
 wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl;
preferably R4 is -SC^M or -POsNfe and more preferably R4 is -SOsM; and M is preferably Na; and
A is preferably bromine. The presently more preferred first intermediate is 2-bromoethane
sulfonate, isolated as crystals.
 (b) The first intermediate is washed with water, acetone or a protic solvent, such as,
without limitation, aqueous methanol, aqueous ethanol, aqueous 2-propanol or aqueous 2-methyl-l-
propanol. For pharmaceutical uses of the Formula II product, acetone or aqueous ethanol is
 (c) The washed first intermediate from step (b) is then reacted in aqueous solution with an alkali metal mecaptan having a base-sensitive labile protective group to form a second intermediate having a Formula (V):
 Z is a base-sensitive labile protective jproup; and wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl; preferably R4 is -SO3M or -PO3M2; and more preferably R4 is -SO3M; and M is preferably Na; and Z is any suitable base-sensitive labile protective group, such as, without lirnitation, acetyl, mesyl or tosyl, and preferably acetyl. The presently preferred alkali metal mecaptan with the base-sensitive labile protective group is sodium thioacetate, and the presently preferred second intermediate is sodium 2-acetylthioethane sulfonate. This step preferably includes adding, preferably with mixing at a rate of about 15 to about 150 rpm, the alkali metal mecaptan having a base-sensitive labile protective group to the aqueous solution of the first intermediate from step (b) over a period of about 15 to about 120 minutes while maintaining a temperature of about 15° C to about 90° C, with agitation for a tune such that the level of impurity is less than about 5%.
 (d) The second intermediate from step (c) is reacted, preferably with mixing ,at a rate of
about 15 to about 150 rpm, in aqueous solution with about 1 to about 3 mol equivalents, preferably ,
about 1.1 to about 1.4 mol equivalent of a strong base, such as, without limitation, NaOH, KOH,
NaaCOa or KjCOa and adjusting the pH of the solution to a pH of about 6.5 to about 8.0 with an
acid, such as, without limitation, acetic acid, oxalic acid or citric acid, preferably acetic acid, or with
a base, such as, without limitation, NaOH, KOH, Na2CO3 or K^COa, preferably NaOH, to form a
third intermediate having a Formula (VI): .
 wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl; preferably R4 is -SO3M or -PO3M2; and more preferably R4 is -SO3M; and M is preferably Na. The presently preferred third intermediate is sodium 2-mercaptoethane sulfonate.  (e) The third intermediate from step (d) is then oxidized in a known manner, such as, without limitation, with oxygen, iodine or silver nitrate, to give an aqueous solution of a compound of Formula II, wherein the lower alkyl is preferably ethyl or propyl, and more preferably ethyl; R5 is preferably -lower alkyl-R6; preferably each of R4 and R6 is -SO3M or -PO3M2; and more preferably each of R4 and R6 is -SO3M; and M is preferably Na. This oxidation step presently is preferably
conducted using an oxygen-containing gas at elevated pressure. The oxidation step is more preferably conducted using air, oxygen at a purity of about 60% to about 95% or a mixture of oxygen and nitrogen where the oxygen is present at about 50% to about 99%, and most preferably air, where the oxygen or oxygen-containing gas is pressurized to about 0.1 MPa to about 10 MPa, at a temperature of about 20°C to about 80°C, preferably about 25°C to about 60°C. The presently preferred product of Formula II is dimesna, namely, disodium 2,2-dithiobis ethane sulfonate.  (f) The aqueous solution of the compound of Formula EL, such as disodium 2,2'-dithiobis ethane sulfonate, is then concentrated by distilling away a portion of the aqueous solution and then cooling the aqueous solution to give crystals of the Formula II compound, such as disodium 2,2'-dithiobis ethane sulfonate crystals.
 (g) The crystals of the compound of Formula II from step (f), such as disodium 2,2'-dithiobis ethane sulfonate crystals, are then washed in a known manner to provide a substantially pure compound of Formula II, such as disodium 2,2'-dithiobis ethane sulfonate.  This process produces substantially pure compounds of Formula II, such as disodium 2,2'-dithiobis ethane sulfonate, in good yield, such as about 60% by weight to about 80% by weight, which is quite a good yield for a one-pot process, after crystallization. To improve the purity of the final product, the starting materials and all reactants should have a purity of at least about 90%, and preferably at least about 95%. Preferably the disulfide of Formula II produced by this process is pharmaceutically active.
 Preferred embodiments will now be described in more detail with reference to the following specific, non-limiting examples.
[0078J Example 1
 Production of sodium 2-bromoethane sulfonate
 After 1018g of 47% hydrobromic acid were added dropwise to 292g of 60% aqueous
sodium isethionate solution, the mixture was heated under reflux and 348g were distilled off at
 The residue was cooled to 50°C and 52g of 47% hydrobromic acid were added, then
further cooled from 50°C to 5°C. The precipitated crystals were filtered out at about 5°C and
washed with 77.1g of 47% hydrobromic acid being cooled to about 5°C and then 17.5g of water
being cooled to about 5°C.
 The crystals were washed twice with a mixture of 408.6g of acetone and 47.4g of water
being cooled to about 5°C, and further washed twice with 221g of acetone being cooled to about
 The crystals were dried under reduced pressure to afford 120g of sodium 2-bromoethane
 Example 2
 Production of disodium 2,2'-dithiobis ethane sulfonate
 To a mixture of 50. Ig of water with 24.4g of thioacetic acid, 50.7g of 25% aqueous
sodium hydroxide solution were added dropwise at 10-30°C. This solution was added dropwise to a
solution of 63.3g of sodium 2-bromoethane sulfonate and 70g of water at 50-70°C and allowed to react at 80-90°C for 2 hours.
 Thereto 54.2g of 25% aqueous sodium hydroxide solution were added and allowed to react at refluxing temperature (about 105°C) until the end of the reaction was confirmed by HPLC. After addition of 3.25g of acetic acid, the reaction mixture was refluxed for 6 hours and then cooled to about 30°C. The pH of the mixture was adjusted to 7.3 with 25% sodium hydroxide solution. Oxygen was allowed to react with 260 mL of aqueous sodium 2-mercapto ethane sulfonate solution obtained above at about 30°C and 0.5-0.6 MPa of oxygen pressure.
 When the end of the reaction was confirmed by HPLC, the reaction was stopped and the mixture was neutralized with acetic acid. The mixture was heated to about 70°C and it was observed that the mixture had been dissolved. After that, the mixture was filtered with a filtering assistant agent (radiolite) and the filtering assistant agent was washed with lOg of water.  The mixture was concentrated under reduced pressure (about 10 kPa) at 70°C. When the amount of the distilled out water became 60g, the concentration was stopped and it was observed
that the mixture remained dissolved at about 75°C. Cooling the mixture, crystallization began at 60 ± 5°C. After aging for about 30 minutes, the mixture was cooled to 25°C and the crystals were aged for 2 hours at 25°C.
 The crystals were filtered out and washed with 24g of water being cooled to 2°C and then 48 mL of 70% aqueous ethanol solution. Drying the crystals at about 70°C afforded 39.1g of substantially pure disodium 2,2'-diihiobis ethane sulfonate crystals. The yield was 77.6% after
crystallization. The purity of the product was 99.4%.
(0091] According to the present invention, compounds of Formula II, such as disodium 2,2'-
dithiobis ethane sulfonate, can be produced by an efficient procedure from available, relatively less
expensive raw compounds in good yield with high purity. The above details are not limitative of the
invention, which is defined by the scope of the following claims.
 It will be appreciated by those skilled in the art that changes could be made to the
embodiments described above without departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the particular embodiments disclosed, but
it is intended to cover modifications within the spirit and scope of the present invention as defined
by the appended claims.
1. A process for preparing disodium 2,2'-dithiobis ethane sulfonate, which comprises:
(a) brominating sodium isethionate in aqueous solution by addition of hydrobromic acid, in the absence of isethionic acid, to form sodium 2-bromoethane sulfonate as a first intermediate;
(b) reacting the first intermediate with sodium thioacetate to form sodium 2- acetylthioethane sulfonate as a second intermediate;
(c) reacting the second intermediate with a strong base to form sodium 2- mercaptoethane sulfonate as a third intermediate;
(d) oxidizing the third intermediate with oxygen at a temperature of 30°C to form disodium 2,2'-dithiobis ethane sulfonate; and
(e) isolating the disodium 2,2' -dithiobis ethane sulfonate.
2. A process as claimed in claim 1, wherein the oxidizing step (d) is conducted at elevated pressure.
3. A process as claimed in claim 1, wherein the strong base is selected from the group consisting of NaOH, KOH, Na2CO3 and K2CO3.
4. A process as claimed in claim 3, wherein the strong base is NaOH.
5. A process as claimed in claim 1, wherein steps (a) and (b) are carried out in aqueous solution.
6. A process as claimed in claim 1, wherein the second intermediate is washed with a solvent selected from the group consisting of water, acetone and a protic solvent, and the washed second intermediate is reacted with the strong base, followed by adjusting the pH with acid or base to a pH of 6.5 to 8.0 to form the third intermediate.
7. A process as claimed in claim 1, wherein the third intermediate is oxidized to form an aqueous solution of disodium 2,2'-dithiobis ethane sulfonate, followed by concentrating the aqueous solution by distilling away a portion of the aqueous solution and then cooling the aqueous solution to give crystals of disodium 2,2'- dithiobis ethane sulfonate, and washing the crystals to provide substantially pure disodium 2,2'-dithiobis ethane sulfonate.
|Indian Patent Application Number||3391/DELNP/2006|
|PG Journal Number||43/2011|
|Date of Filing||13-Jun-2006|
|Name of Patentee||BIONUMERIC PHARMACEUTICALS, INC|
|Applicant Address||8122 DATAPOINT DRIVE, SUITE 1250, SAN ANTONIO, TX 78229, UNITED STATES OF AMERICA.|
|PCT International Classification Number||C07C 309/00|
|PCT International Application Number||PCT/US2004/042533|
|PCT International Filing date||2004-12-17|