BACKGROUND OF THE INVENTION [0002] Dithiocarbamates have been found to have numerous pharmaceutical utilities, for example as nitric oxide scavengers for the treatment of inflammatory and infectious diseases (See, for example, the recent work of Lai, as described in U. S. Pat. Nos. 5,714, 815,5, 756,540, 5,757, 532, and 5,847, 004, the contents of each of which are hereby incorporated by reference in their entirety). Disulfide derivatives of dithiocarbamates have been found to be especially useful for such purposes (see, for example, U. S. Pat. No.

6,093, 743, the entire contents of which are hereby incorporated by reference).

[0003] Prior to the discovery of pharmaceutical utilities for dithiocarbamates and disulfide derivatives thereof, more traditional uses thereof include use in chemical or commercial endeavors, for example, for precipitating metals in chemical analysis or for synthesis of heterocyclic compounds (Thorn & Ludwig, The Dithiocarbamates and Related Compounds, Elsevier, Amsterdam, 1962, pages 61-126). These more traditional uses typically do not require the attributes most desired for pharmaceutical-grade dithiocarbamates and disulfide derivatives thereof, such as sterility, purity and stable, fine particulate form. The traditional methods of synthesizing dithiocarbamates and disulfide derivatives thereof, are, therefore, unsuitable for preparation of pharmaceutical grade materials.

[0004] Accordingly, there is a need for new and better methods for producing pharmaceutical-grade and/or sterile dithiocarbamates and disulfide derivatives thereof, as a finely divided particulate.

SUMMARY OF THE INVENTION [0005] In accordance with the present invention, there are provided methods for producing pharmaceutical-grade dithiocarbamates and disulfide derivatives thereof (also known in the art as thiuram disulfides). Invention methods are preferably conducted under sterile conditions, thereby producing a sterile pharmaceutical-grade disulfide derivative of a dithiocarbamate. In one embodiment, the invention method comprises vigorously contacting a mixture of carbon disulfide, at least one secondary amine, and a pharmaceutical acceptable diluent in a mixing zone under an inert gas atmosphere, wherein the diluent is a solvent for the carbon disulfide, but not for the dithiocarbamate, thereby facilitating recovery of the dithiocarbamate intermediate. The invention method further comprises contacting the resulting reaction mixture with an oxidizing agent under conditions suitable to convert dithiocarbamate into the disulfide derivative thereof.

[0006] In another embodiment, the invention synthesis method comprises vigorously contacting a mixture of carbon disulfide, at least one secondary amine and a pharmaceutically acceptable diluent that is a solvent for the carbon disulfide, but not for the dithiocarbamate, in a mixing zone under an inert gas atmosphere and under conditions suitable for producing the dithiocarbamate.

The invention synthesis method further comprises contacting the resulting reaction mixture with an oxidizing agent under conditions suitable to convert dithiocarbamate into the disulfide derivative thereof, and thereafter separating the resulting disulfide from the reaction mixture.

[0007] The invention method optionally further comprises vigorously stirring a solution of a disulfide of a dithiocarbamate in pharmaceutical-grade water in a second mixing zone, while adding pharmaceutical-grade ethanol or acetone thereto under conditions suitable for forming a suspension containing a finely-divided precipitate of a disulfide of a dithiocarbamate therein (in amorphous or crystalline form), and separating the finely divided precipitate from the suspension, for example, by filtration or other suitable means.

BRIEF DESCRIPTION OF THE DRAWING [0008] FIG. 1 is a schematic diagram illustrating the invention method for producing a pharmaceutical-grade disulfide of a dithiocarbamate starting with carbon disulfide and a secondary amine. To a continuously stirred aqueous solution (optionally containing an added diluent such as ethanol) of secondary amine in a cooled reaction vessel is added carbon disulfide (also optionally containing diluent, e. g., ethanol). The resulting dithiocarbamate product is then subjected to oxidizing conditions suitable to convert the dithiocarbamate into a disulfide derivative thereof.

DETAILED DESCRIPTION OF THE INVENTION [0009] In accordance with the present invention, there are provided methods for producing pharmaceutical-grade disulfide derivatives of dithiocarbamates (also known in the art as thiuram disulfides). Invention methods are preferably conducted under sterile conditions, thereby producing sterile pharmaceutical grade disulfide derivatives of dithiocarbamate.

[0010] In one embodiment, the invention method comprises contacting a mixture of carbon disulfide, at least one secondary amine, and a pharmaceutically acceptable diluent that is a solvent for the carbon disulfide, but not for the dithiocarbamate, in a mixing zone under an inert gas atmosphere and under conditions suitable for producing dithiocarbamate, thereby facilitating recovery of the dithiocarbamate intermediate. The invention method optionally further comprises separating the resulting dithiocarbamate from the mixture.

The invention methods for producing a pharmaceutically acceptable dithiocarbamate can be performed either as a continuous process or as a batch process.

[0011] The resulting dithiocarbamate is then contacted with an oxidizing agent under conditions suitable to oxidatively couple dithiocarbamate to form a disulfide derivative thereof. The resulting disulfide derivative is then optionally separated from the reaction mixture.

[0012] Among the secondary amines suitable for use in preparation of pharmaceutical acceptable dithiocarbamates and disulfide derivatives thereof are those having the formula: RiR2NH, [0013] wherein each Ri and R2 is independentiy Ci up to C18 hydrocarbyl, substituted hydrocarbyl, heterocyclic, substituted heterocyclic, heteroaryl, substituted heteroaryl, aroyl, substituted aroyl, acyl, substituted acyl, or Ri and R2 can cooperate to form a 5-, 6-or 7-membered ring including N, Ri and R2, or [0014] Ri or R2 is a divalent moiety selected from the group consisting of alkylen, substituted alkylene, oxyalkylene, substituted oxyalkylene, alkenylene, substituted alkenylene, arylene, substituted arylene, alkarylene, substituted alkarylene, aralkylene and substituted aralkylene, wherein said divalent moiety serves as the same substituent for two dithiocarbamate molecules, thereby linking said molecules together so as to form a bis (dithiocarbamate) species, and the like, and suitable combinations thereof.

[0015] For example, the secondary amine can have the formula R, R2N H, wherein each of Ri and R2 is Ci up to C, 2 alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl or substituted alkynyl, wherein the substituents are selected from carboxyl,--C (O) H, oxyacyl, phenol, phenoxy, pyridinyl, pyrrolidinyl, amino, amido, hydroxy, nitro or sulfuryl. For example Ri can be Cl up to C8 alkyl or substituted alkyl, wherein the substituents are carboxyl, acetyl, pyridinyl, pyrrolidinyl, amino, amido, hydroxy or nitro, and R2 is either Cl up to Ce alkyl or substituted alkyl, or R2 can cooperate with Ri to form a 5-, 6-or 7- membered ring including N, R2 and Ri. In the secondary amines presently preferred for use in the practice of invention method (s) for the preparation of dithiocarbamates and disulfide derivatives thereof, Ri is C2 up to C8 alkyl or substituted alkyl, wherein the substituents are selected from carboxyl, acetyl, amido or hydroxy, and R2 is C1 up to C4 alkyl or substituted alkyl.

[0016] To avoid contamination of the dithiocarbamate product with a solvent that is not pharmaceutically acceptable and to assist in precipitation of the dithiocarbamate from the reaction mixture as a stable solid (in amorphous or crystalline form), the diluent generally comprises suitable organic media such as ethanol or acetone, and excludes such pharmaceutical inappropriate solvents as methanol. For example, the carbon disulfide can be introduced into the mixing zone neat, or as a solution of carbon disulfide in ethanol, for example in absolute ethanol. The diluent can further contain water and a suitable base, such as sodium hydroxide, for formation of a dithiocarbamate salt. Since alkali metal salts of dithiocarbamates are soluble in water, it is preferred that the cation be an alkali metal cation.

[0017] In a preferred embodiment of the invention method for producing a pharmaceutically acceptable dithiocarbamate, the carbon disulfide is added to the reaction mixture dissolved in aqueous ethanol or aqueous acetone. As recognized by those of skill in the art, it is preferred that carbon disulfide be employed in excess. Thus, the ratio of secondary amine to disulfide can be as high as about 1: 2, typically falling in the range of about 1-2: 2, with a ratio of about 1: 1.2 presently preferred.

[0018] Carbon disulfide and secondary amine are vigorously contacted in a mixing zone in accordance with invention methods. The vigorous contacting can be accomplished employing any means known in the art, such as centrifugation, mixing, stirring, sparging, vigorous bubbling of an inert gas through the reaction mixture, and the like, or a combination of any two or more thereof. For example, the mixing can be accomplished by any magnetic or mechanical stirring device capable of vigorously stirring the slurry formed by precipitation of the dithiocarbamate in the reaction zone. In one embodiment, the stirring device is magnetic and is capable of achieving stirring speeds in the range of about 10 rpm up to about 1000 rpm.

[0019] Optionally, dithiocarbamate can be precipitated prior to further treatment. If so desired, conditions suitable for precipitating the dithiocarbamate include cooling the reaction mixture, preferably to a temperature of from about minus 10°C. to about 20°C. at atmospheric pressure. The cooling of the reaction mixture can be accomplished by any method known in the art, including, but not limited to, submerging a reaction vessel containing the mixture in an ice water or ice/salt water bath. Alternatively, the reaction vessel can be refrigerated using known technologies.

[0020] The conditions suitable for separation of the dithiocarbamate from the reaction mixture optionally further include subjecting the reaction mixture to a reduced pressure (i. e. , reduced with respect to the pressure in the mixing zone), for example, by passing the reaction mixture through a separation zone, such as a separation vessel, that can be maintained at a reduced pressure.

[0021] The initially produced dithiocarbamate, whether enriched by precipitation or other means, or used directly as produced, is then contacted with an oxidizing agent under conditions suitable to oxidatively couple dithiocarbamate to form a disulfide derivative thereof. Those of skill in the art can readily identify oxidizing agents suitable for such purpose. Exemplary oxidizing agents include halogens (such as 12) plus an alkali metal salt (such as Nal or Kl), hydrogen peroxide, ammonium persulfate, potassium ferricyanide, sodium hypochloride (NaOCI), and the like. Presently preferred oxidizing agents include agueous 12/KI or 12/Nal combinations.

[0022] Oxidative coupling of dithiocarbamates to produce disulfide derivatives thereof is generally carried out under mild conditions, e. g. , at temperatures in the range of about-10 up to about 30°C. Reaction times are generally relatively fast, typically limited by the rate of oxidant addition so as to maintain the reaction mixture at the desired temperature.

[0023] The resulting disulfide derivatives of dithiocarbamates are readily recovered from the reaction medium employing standard techniques such as precipitation, filtration, centrifugation, crystallization, or the like.

[0024] When prepared according to the invention methods, the disulfide derivatives of dithiocarbamates are in the form of a particulate solid, preferably a finely divided particulate solid having a major dimension in the size range from about 100/im to about 1 cm, or smaller (in amorphous or crystalline form).

Separation of the particulate disulfide derivatives of dithiocarbamates from the reaction mixture can also be carried out by passage of the reaction mixture through a filter, a screen, or a combination thereof so as to collect the disulfide derivatives of a dithiocarbamate as a filter cake. A screen or filter having a pore size generally in the range from about 0. 1, um, for example, typically in the range from about 10, um to about 50, um, and preferably in the range from about 10 /im to about 20, um, is particularly useful for obtaining a finely divided disulfide derivative of a dithiocarbamate product with pharmaceutical utility.

[0025] The invention method for preparing pharmaceutical-grade disulfide derivatives of a dithiocarbamate optionally further comprises washing the precipitated disulfides of a dithiocarbamate with ethanol having an ethanol content in the range from about 70% ethanol to absolute ethanol. For example, during the washing, the ethanol content can be increased from about 70% ethanol to absolute ethanol, with the increase being made gradually or in incremental steps.

[0026] In another embodiment of the invention methods for producing pharmaceutically acceptable disulfide derivatives of dithiocarbamates, the method may also further comprise replacing the atmosphere in the first and/or second reaction zone (i. e. , the zone wherein carbon disulfide and secondary amine are contacted or where oxidative coupling is carried out) with an inert gas, such as nitrogen, argon, and the like, or a combination thereof. For example, the inert gas can be introduced into the mixing zone by a continuous purge at a flow rate generally from about 0.1 liters to about 300 liters per minute.

Typically flow rates may fall in the range of about 30 liters to about 100 liters per minute, or from about 0.1 liter to about 50 liters per minute. Flow rates of from about 1. 0 liter to about 20 liters per minute are presently preferred when continuous or semi-continuous purge is employed. The mixing zone is optionally substantially closed to facilitate use of the inert purge gas. Alternatively, an inert gas atmosphere can be introduced by evacuating the reaction vessel, then introducing an inert atmosphere in place of the initially removed reaction atmosphere. As recognized by those of skill in the art, this procedure may desirably be repeated several times to encourage removal of residual amounts of oxygen or other impurities which may be dissolved in the reaction medium.

[0027] The initial step of the invention method for the synthesis of disulfide derivatives of dithiocarbamates (i. e. , preparation of the dithiocarbamate precursor thereof) can be carried out employing methods known in the art. A presently preferred method for such synthesis is described by Vassilev et al, in U. S. Patent No. 6,124, 349, the entire contents of which are hereby incorporated by reference herein.

[0028] The initially produced dithiocarbamate is then contacted with an aqueous mixture of 2/Na ! under conditions suitable to oxidatively couple dithiocarbamate to a disulfide derivative thereof.

[0029] In an alternative embodiment, the invention method further comprises a purification step to further purify the disulfide derivative of a dithiocarbamate synthesized as described above by the invention synthesis method (s). In this embodiment, the invention synthesis method further comprises vigorously stirring in a separate mixing zone a solution of the disulfide derivative of a dithiocarbamate in pharmaceutical-grade water while adding pharmaceutical-grade ethanol or acetone thereto under conditions suitable for forming a suspension containing a finely-divided precipitate of a disulfide derivative of a dithiocarbamate therein (in amorphous or crystalline form), and separating a finely divided precipitate of a disulfide derivative of a dithiocarbamate from the suspension. Dissolving the precipitate in pharmaceutical-grade water and contacting the solution with a pharmaceutical- grade ethanol or acetone, preferably absolute ethanol, aids in obtaining a sterile product and eliminates undesirable by-products from the precipitate.

[0030] Alternatively, this purification step can be performed independently of the above described method for producing a pharmaceutical-grade disulfide derivative of a dithiocarbamate by using any particulate disulfide derivative of a dithiocarbamate (in amorphous or crystalline form), as the feed. When performed independently, the invention purification method comprises vigorously stirring in a mixing zone a solution of a disulfide derivative of a dithiocarbamate in pharmaceutical-grade water while adding pharmaceutical-grade ethanol or acetone thereto under conditions suitable for forming a suspension containing a finely-divided precipitate of a disulfide derivative of a dithiocarbamate therein (in amorphous or crystalline form), and separating the resulting precipitate from the suspension.

[0031] Among the feed disulfides suitable for use in the invention purification methods are those having the structure (1) as follows : R, R2N-C (S)-S-S-C (S)-NR, R2 (I) [0032] wherein: [0033] each Ri and R2 is independently selected from Cl up to C18 hydrocarbyl, substituted hydrocarbyl, heterocyclic, substituted heterocyclic, heteroaryl, substituted heteroaryl, aroyl, substituted aroyl, acyl, substituted acyl, or Ri and R2 can cooperate to form a 5-, 6-or 7-membered ring including N, Ri and R2, or [0034] Ri or R2 is a divalent moiety selected from the group consisting of alkylen, substituted alkylen, oxyalkylene, substituted oxyalkylene, cycloalkylene, substituted cycloalkylene, alkenylene, substituted alkenylene, arylen, substituted arylene, alkarylene, substituted alkarylene, aralkylene and substituted aralkylene, wherein said divalent moiety serves as the same substituent for two dithiocarbamate structures, thereby linking said structures together so as to form a bis (dithiocarbamate) species, [0035] Presently preferred disulfide compounds having generic structure I are those wherein: [0036] Ri and/or R2 is a divalent moiety selected from the group consisting of alkylen, substituted alkylen, oxyalkylene, substituted oxyalkylene, alkenylene, substituted alkenylene, arylen, substituted arylen, alkarylene, substituted alkarylene, aralkylene and substituted aralkylene, wherein said divalent moiety serves as the same substituent for two dithiocarbamate structures, thereby linking said structures together so as to form a bis (dithiocarbamate) species.

[0037] Additional preferred disulfide compounds having generic structure I are those wherein: [0038] Ri and/or R2 is a polyvalent moiety, wherein said polyvalent moiety serves as the same substituent for a plurality of dithiocarbamate structures, thereby linking said structures together so as to form a poly (dithiocarbamate) species.

[0039] Still further preferred disulfide compounds having generic structure I are those wherein: [0040] Each of Ri and R2=a Ci up to C12 alkyl, substituted allcyl, alkenyl, substituted alkenyl, alkynyl or substituted alkynyl, wherein the substituents are selected from carboxyl,-C (O) H, oxyacyl, phenol, phenoxy, pyridinyl, pyrrolidinyl, amino, amido, hydroxy, nitro or sulfuryl.

[0041] Additional preferred disulfide compounds having generic structure I are those wherein: [0042] Ri is selected from C2 up to C8 alkyl or substituted alkyl, wherein the substituents are selected from carboxyl, acetyl, pyridinyl, pyrrolidinyl, amino, amido, hydroxy or nitro, and [0043] R2 is selected from C, up to C8 alkyl or substituted alkyl.

[0044] As employed herein,"hydrocarbyl"comprises any organic radical wherein the backbone thereof comprises carbon and hydrogen only. Thus, hydrocarbyl embraces alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, aryl, alkylaryl, arylalkyl, arylalkenyl, alkenyl aryl, arylalkynyl, alkynylaryl, and the like.

[0045] As employed herein, "substituted hydrocarbyl"comprises any of the above-referenced hydrocarbyl groups further bearing one or more substituents selected from hydroxy, alkoxy (of a lower alkyl group), mercapto (of a lower alkyl group), cycloalkyl, substituted cycloalkyl, heterocyclic, substituted heterocyclic, aryl, substituted aryl, heteroaryl, substituted heteroaryl, aryloxy, substituted aryloxy, halogen, trifluoromethyl, cyano, nitro, nitrone, amino, amido,-C (O) H, acyl, oxyacyl, carboxyl, carbamate, dithiocarbamoyl, sulfonyl, sulfonamide, sulfuryl, and the like.

[0046] As employed herein,"alkyl"refers to saturated straight or branched chain hydrocarbon radical having in the range of 1 up to about 20 carbon atoms."Lower alkyl"refers to alkyl groups having in the range of 1 up to about 5 carbon atoms."Substituted alkyl"refers to alkyl groups further bearing one or more substituents as set forth above.

[0047] As employed herein,"cycloalkyl"refers to a cyclic ring-containing groups containing in the range of about 3 up to about 8 carbon atoms, and "substituted cycloalkyl"refers to cycloalkyl groups further bearing one or more substituents as set forth above. As employed herein,"cycloalkylene"refers to divalent ring-containing groups containing in the range of about 3 up to about 8 carbon atoms, and"substituted cycloalkylene"refers to cycloalkylene groups further bearing one or more substituents as set forth above.

[0048] As employed herein,"alkylene"refers to saturated, divalent straight or branched chain hydrocarbyl groups typically having in the range of about 2 up to about 12 carbon atoms, and"substituted alkylene"refers to alkylen groups further bearing one or more substituents as set forth above.

[0049] As employed herein,"oxyalkylene"refers to saturated, divalent straight or branched chain oxygen-containing hydrocarbon radicals typically having in the range of about 2 up to about 12 carbon atoms, and"substituted oxyalkylene"refers to oxyalkylene groups further bearing one or many substituents as set forth above.

[0050] As employed herein,"alkenyl"refers to straight or branched chain hydrocarbyl groups having at least one carbon-carbon double bond, and having in the range of about 2 up to 12 carbon atoms, and"substituted alkenyl"refers to alkenyl groups further bearing one or more substituents as set forth above.

[0051] As employed herein,"alkenylene"refers to divalent straight or branched chain hydrocarbyl groups having at least one carbon-carbon double bond, and typically having in the range of about 1 up to 12 carbon atoms, and "substituted alkenylene"refers to alkenylene groups further bearing one or more substituents as set forth above.

[0052] As employed herein,"alkenylene"refers to divalent straight or branched chain hydrocarbyl groups having at least one carbon-carbon double bond, and typically having in the range of about 2 up to 12 carbon atoms, and "substituted alkenylene"refers to alkenylene groups further bearing one or more substituents as set forth above.

[0053] As employed herein,"alkynyl"refers to straight or branched chain hydrocarbyl groups having at least one carbon-carbon triple bond, and having in the range of about 2 up to 12 carbon atoms, and"substituted alkynyl"refers to alkynyl groups further bearing one or more substituents as set forth above.

[0054] As employed herein,"aryl"refers to aromatic groups having in the range of 6 up to 14 carbon atoms and"substituted aryl"refers to aryl groups further bearing one or more substituents as set forth above.

[0055] As employed herein,"heteroaryl"refers to aromatic groups having in the range of 4 up to about 13 carbon atoms, and at least one heteroatom selected from O, N, S, or the like ; and"substituted heteroaryl"refers to heteroaryl groups further bearing one or more substituents as set forth above.

[0056] As employed herein,"alkylaryl"refers to alkyl-substituted aryl groups and"substituted alkylaryl"refers to alkylaryl groups further bearing one or more substituents as set forth above.

[0057] As employed herein,"arylalkyl"refers to aryl-substituted alkyl groups and"substituted arylalkyl"refers to arylalkyl groups further bearing one or more substituents as set forth above.

[0058] As employed herein,"arylalkenyl"refers to aryl-substituted alkenyl groups and"substituted arylalkenyl"refers to arylalkenyl groups further bearing one or more substituents as set forth above.

[0059] As employed herein,"alkenylaryl"refers to alkenyl-substituted aryl groups and"substituted alkenylaryl"refers to alkenylaryl groups further bearing one or more substituents as set forth above.

[0060] As employed herein,"arylalkynyl"refers to aryl-substituted alkynyl groups and"substituted arylalkynyl"refers to arylalkynyl groups further bearing one or more substituents as set forth above.

[0061] As employed herein,"alkynylaryl"refers to alkynyl-substituted aryl groups and"substituted alkynylaryl"refers to alkynylaryl groups further bearing one or more substituents as set forth above.

[0062] As employed herein,"arylene"refers to divalent aromatic groups typically having in the range of 6 up to 14 carbon atoms and"substituted arylene"refers to arylene groups further bearing one or more substituents as set forth above.

[0063] As employed herein,"aralkylene"refers to aryl-substituted divalent alkyl groups typically having in the range of about 7 up to 16 carbon atoms and "substituted aralkylene"refers to aralkylene groups further bearing one or more substituents as set forth above.

[0064] As employed herein,"aralkylene"refers to aryl-substituted divalent alkyl groups typically having in the range of about 7 up to 16 carbon atoms and "substituted aralkylene"refers to aralkylene groups further bearing one or more substituents as set forth above.

[0065] As employed herein,"aralkenylene"refers to aryl-substituted divalent alkenyl groups typically having in the range of about 8 up to 16 carbon atoms and"substituted aralkenylene"refers to aralkenylene groups further bearing one or more substituents as set forth above.

[0066] As employed herein,"aralkynylene"refers to aryl-substituted divalent alkynyl groups typically having in the range of about 8 up to 16 carbon atoms and"substituted aralkynylene"refers to aralkynylene group further bearing one or more substituents as set forth above.

[0067] As employed herein,"heterocyclic"refers to cyclic (i. e. , ring- containing) groups containing one or more heteroatoms (e. g. , N, O, S, or the like) as part of the ring structure, and having in the range of 3 up to 14 carbon atoms and"substituted heterocyclic"refers to heterocyclic groups further bearing one or more substituents as set forth above.

[0068] As employed herein,"heterocycloalkylene"refers to divalent cyclic (i. e. , ring-containing) groups containing one or more heteroatoms (e. g. , N, 0, S, or the like) as part of the ring structure, and having in the range of 3 up to 14 carbon atoms and"substituted heterocycloalkylene"refers to heterocycloalkylene groups further bearing one or more substituents as set forth above.

[0069] As employed herein,"aroyl"refers to aryl-carbonyl species such as benzoyl and"substituted aroyl"refers to aroyl groups further bearing one or more substituents as set forth above.

[0070] As employed herein,"acyl"refers to alkyl-carbonyl species.

[0071] As employed herein,"halogen"refers to fluoride, chloride, bromide or iodide atoms.

[0072] In the practice of the invention method for obtaining sterile pharmaceutical-grade disulfide derivatives of dithiocarbamates, the separating can involve passage of the precipitate (in amorphous or crystalline form) through a separation zone maintained at reduced pressure. The separation can further involve passage of the suspension containing the precipitate (e. g. in the separation zone) through a filter, a screen, or a combination thereof, as described above with respect to the invention synthesis methods.

[0073] The method for producing sterile disulfide derivatives of a dithiocarbamate can further comprise washing the separated precipitate (in amorphous or crystalline form), for example, in the separation zone, with a sterile wash ethanol having an ethanol content in the range from about 70% ethanol to absolute ethanol. In one embodiment, during the washing the ethanol content in the wash ethanol is increased from about 70% ethanol to absolute ethanol, for example, either gradually or in one or more incremental steps. The wash ethanol aids in sterilizing and drying the disulfide product.

[0074] To further aid in obtaining a sterile product, each of the solution of disulfide derivative of a dithiocarbamate and the ethanol can be sterilized by passage into the mixing zone through a sterilizing filter, such as is known in the art, for example, membrane filters of mixed cellulose esters and polysulphones (Millipore, Bedford, Mass. ). Such sterilizing filters generally have pore sizes small enough to prohibit passage of microbes through the filter while allowing passage of dissolved small molecules, such as ethahol and the disulfides disclosed herein, for example pore sizes in the range of about 0. 2, um to about 75, um are typical. The wash ethanol can also be sterilized by passage into the separation zone through such a sterilizing filter.

[0075] The invention method for producing sterile disulfide derivatives of a dithiocarbamate can further comprise drying the separated precipitate (in amorphous or crystalline form) to constant weight, for example by passage of a sterile inert gas over the separated precipitate in a separation zone. The inert gas can be made sterile by passage into the separation zone through a sterilizing filter.

[0076] The invention method for producing sterile disulfide derivatives of a dithiocarbamate can also further comprise aseptic transfer, for example in a Class 100 sterile room, of a unit dose of dried sterile disulfide derivatives of a dithiocarbamate (in amorphous or crystalline form) into individual sterile vials.

Usually, a unit dose of the pharmaceutical-grade disulfide derivatives of a dithiocarbamate is in the range from about 100 mg to about 10 grams, with typical unit doses falling in the range of about 200 mg to about 3 grams.

[0077] The invention will now be described in greater detail by reference to the following non-limiting example.

EXAMPLE [0078] Preparation of pharmaceutical-grade disulfide derivative of L- proline dithiocarbamate (LPD).

[0079] Part 1 : synthesis of L-proline dithiocarbamate (LPD).

Pharmaceutical-grade LPD was prepared using the invention process. A solution containing 0.3 kg of sodium hydroxide dissolved in 1.0 liter of deionized water (DIW) was prepared and injected into a 27 liter reaction vessel. The sodium hydroxide solution in the reaction vessel was cooled to room temperature with an ice/salt bath, and then 0.5 kg of L-prolin was added to the alkaline solution and dissolved with stirring, making a solution having a 1: 2 ratio of L-proline to NaOH. Cooling of the solution was continued to a temperature of-10°C to 10°C. The reaction medium was then diluted with about 2 liters of ethanol. The reaction vessel was purged with nitrogen gas and kept under a constant nitrogen atmosphere during the remainder of the synthesis process.

[0080] A separate feed of 255 ml of carbon disulfide was slowly added into the cold solution of L-prolin in NaOH in the reaction vessel with stirring over a period of about 20 to 25 minutes. Cooling and stirring of the reaction mixture was continued for an additional 20 minutes after all of the CS2 had been introduced into the reaction vessel. The dithiocarbamate contained in this reaction product is suitable for conversion directly into the desired disulfide derivative. Alternatively, if desired (e. g., for long-term storage or the like), the dithiocarbamate product could be isolated at this point.

[0081] If dithiocarbamate is to be isolated at this point, then 15 liters of ethanol is introduced into the reaction vessel and stirring continued for an additional two hours. To obtain the product dithiocarbamate as a solid, the reaction mixture containing the LPD precipitate is passed through a filter for collection while a vacuum suction is applied across the filter and while the filter cake is washed with wash ethanol having a progressively higher ethanol content: first, with 5 liters of 70% ethanol, then with 10 liters of 95% ethanol, and then with 4 liters of absolute ethanol. To dry the collected solid, the vacuum is maintained for three hours, and then the LPD was air dried to assure desiccation.

[0082] Part li : Oxidative Coupling of LPD. The LPD prepared in Part I above was oxidatively coupled by diluting the above described reaction mixture with about 1.3 litters of DIW, then adding about 2.2 liters of an 12/Nal solution prepared as follows. This addition is carried out at a rate suitable to maintain the reaction medium at the desired temperature.

[0083] First, a Nal solution is prepared by dissolving 0.6 kg Nal in about 2L of DIW. To this solution is added 0.5 kg of i2. The resulting solution is used as described in the preceding paragraph.

[0084] Part III : Purification of disulfide derivative of LPD. The disulfide derivative of LPD prepared in Part II above was purified by dilution in a suitable non-solvent, e. g. , acetone or ethanol. For example, 30 liters of acetone can be added with continuous stirring. The precipitated LPD can then be stirred for an additional 1-2 hours to facilitate production of relatively pure precipitate, which can then be passed through a filter for collection while a vacuum suction was applied across the filter and while the filter cake is washed with progressively purer ethanol : first with 5 liters of 70% ethanol, then with 10 liters of 95% ethanol, and then with 4 liters of absolute ethanol. To dry the collected solid, the vacuum is maintained for three hours, and then the LPD disulfide is air dried to assure desiccation.

[0085] Part IV : Sterilization of LPD disulfide. The LPD disulfide prepared in Part III above can be sterilized as follows. The purified LPD disulfide is dissolved in up to 7 liters of water and delivered through a sterilizing filter having a pore size of 0. 2, um into a sterile precipitation vessel. To precipitate the MGD disulfide, up to 20 liters of acetone or 95% ethanol is delivered into the sterile precipitation vessel through a sterilizing filter having a pore size of 0. 2, um.

Then the precipitated LPD disulfide is filtered through a glass filter having a pore size of 50 to 75, um while the filter cake was washed under vacuum as described above, except that the acetone or ethanol is delivered into the precipitation/filtration system through a sterilizing filter having a pore size of 0.2 , um. The filter cake of precipitated sterile LPD disulfide is dried up to a constant weight (to assure complete desiccation) by applying a flow of nitrogen gas through a sterilizing filter.

[0086] The dried LPD disulfide is transferred under sterile conditions into a Class 100 sterile room for aseptic transfer of a unit dose (100 mg to 10 grams) into individual sterile glass vials and stored at room temperature.

[0087] It will be apparent to those skilled in the art that various changes may be made in the invention without departing from the spirit and scope thereof, and therefore, the invention encompasses embodiments in addition to those specifically disclosed in the specification, but only as indicated in the appended claims.