LOWCOST, HIGH YIELD SYNTHESIS OF NEVIRAPINE

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of United States Provisional patent application

62/165,527, filed January 20, 2015, the complete contents of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention generally relates to improved methods of producing the HIV drug substance, nevirapine. In particular, the invention provides cost effective, high yield synthetic methods for preparing nevirapine building blocks such as 2-chloro-3-amino-4-picoline (CAPIC) and 2-cyclopropyl amino nicotinate (Me-CAN), as well as improvements in other steps of nevirapine synthesis.

Background

Nevirapine (Figure 1) is currently a major component of front line treatment in HIV combination drug therapy. Though its prominence as a frontline therapy may be supplemented by new drug alternatives, the World Health Organization forecasts that over 600 metric tons per year will be required to treat existing patients for the foreseeable future. Therefore, a cost effective process is required to produce nevirapine.

Nevirapine has been made commercially by at least two alternative reaction pathways. The first generation method that was used for the nevirapine launch in 1996, described in US 5620974. employed 2-chloro-nicotinic acid and 2-chloro-3-amino-4-picoline (CAPIC) as starting materials. Unfortunately, the overall yield of this process is only about 59%.

A second generation method was developed that uses 2-cyclopropylamino-nicotinic acid (2-CAN) as an alternative starting material (US 6680383) and is provided in Scheme 2. Unfortunately, the overall yield for this expensive second generation method is only about 68%. It would be of great benefit to have available less expensive and higher yielding methods of synthesizing nevirapine.

A key to providing less expensive, higher yielding methods of producing nevirapine is to provide improved methods for synthesizing starting materials such as 2-chloro-3-amino-4-picoline (CAPIC) and 2-cyclopropylamino-nicotinic acid (2-CAN). CAPIC has been made commercially by at least two alternative reaction pathways. The first method that was used for the nevirapine launch in 1996 (described in issued US patent 5686618) employed 2,5-dichloro-3-cyano-4-picoline (DICNIL) as a starting material. This method has the advantage of a commercially available starting material in DICNIL. However, this method suffers from high raw material cost, poor atom economy and has significant manufacturing cost due to the numerous intermediate isolations and unit operations. The second method was developed by Boehringer-Ingelheim Pharmaceuticals (US 7282583) several years after the nevirapine launch. The method uses 4,4-dimethoxy-2-butanone (DMB) as a starting material in a multi-step synthesis.

The current commercial preparation of 2-CAN is a two-step process. The first step is the formation of 2-cyclopropylamino nicotinonitrile from 2-chloronicotinonitrile. The process requires approximately 4 equivalents of cyclopropylamine (CPA) which is a major cost driver for this method. The isolated product from this reaction is then subjected to hydrolysis conditions in which the nitrile is converted to the corresponding acid using aqueous alcoholic potassium hydroxide at reflux temperature. The 2-CAN is isolated as a Zwitter ion. The overall yield of this two-step process is 70%.

It would also be of great benefit to have available improved, less costly methods of synthesizing CAPIC and 2-CAN.

SUMMARY OF THE INVENTION

Other features and advantages of the present invention will be set forth in the description of invention that follows, and in part will be apparent from the description or may be learned by practice of the invention. The invention will be realized and attained by the compositions and methods particularly pointed out in the written description and claims hereof.

New cost effective methods of producing the HIV drug substance, nevirapine are described herein. According to the methods, cost and unit operation savings are realized, for example, by using new high yield synthetic routes for producing the nevirapine building blocks CAPIC, 2-CAN and Me-CAN. Steps of the synthesis are streamlined and yet result in very high yields so that overall, the cost of manufacturing the building blocks and nevirapine is significantly reduced.

It is an object of this invention to provide methods of preparing nevirapine. The methods comprise steps of i) reacting 2-chloro-3-amino-4-picoline (CAPIC) and a

cyclopropylaminonicotinate (CAN) ester in a suitable solvent under basic conditions to form 2-(cyclopropylamino) nicotinamido-3 ^' -amino-2'-chloro-4'-methylpyridine (CYCLOR); and ii) heating CYCLOR formed in the step of reacting in the suitable solvent under basic conditions to effect ring closure and form the nevirapine. In some aspect, the suitable solvent is diglyme and a suitable base (to render the reaction basic) is NaH. In other aspects, the method includes a step of isolating and/or purifying the nevirapine. In further aspects, the CAN ester is Me-CAN.

The invention also provides methods of preparing 2-chloro-3-amino-4-methyl pyridine (CAPIC). The methods comprise steps of i) in a non-aqueous solvent, reacting an enamine so as to form 2-chloro-3-cyano-4-methylpyridine (CYCIC) by ring closure with chlorination; ii) in an aqueous solvent, hydrolyzing CYCIC to form 2-chloro-3-amido-4-methyl pyridine (COMAD); and iii) reacting COMAD by a Hoffman rearrangement to form CAPIC. In some aspects, the non-aqueous solvent is toluene. In some aspects, the methods further comprise steps of forming the enamine by reacting acetone with malononitrile to form

alkylidene-malonitrile, and reacting said alkylidene-malonitrile with acetic anyhydride and dimethylformamide dimethyl sulfate (DMF-DMS) adduct or dimethylformamide dimethyl acetal (DMF-DMA) to form the enamine. In some aspects, both reacting steps are performed in non-aqueous solvent. In some aspects, the non-aqueous solvent is toluene. In further aspects, the methods comprise steps of isolating CYCIC, isolating COMAD, and isolating CAPIC.

The invention also provides methods of preparing a 2-CAN ester. These methods include steps of i) reacting, at a temperature of at least 140 °C under pressure, a reaction mixture comprising one equivalent of 2-chloronicotinonitrile, one equivalent of

cyclopropylamine (CPA) and a solvent to form 2-cyclopropylamine nicotinonitrile; ii) adjusting the pH of the reaction mixture to at least 14; iii) heating the reaction mixture to a temperature of at least 80 °C under reflux conditions to form the 2-CAN; iv) cooling the reaction mixture and adjusting the pH so as to precipitate the 2-CAN; v) reacting the 2-CAN with a chloride donor to form an acid chloride of the 2-CAN; and vi) reacting the acid chloride of the 2-CAN with an alkyl donor to form a 2-CAN ester. In some aspects, the methods further comprise a step of isolating the 2-CAN. In other aspects, the methods included a step of isolating the 2-CAN ester. In yet other aspects, the pressure is about 60 psi. In some aspects, the alkyl donor is a methyl donor and the 2-CAN ester is Me-CAN.

In addition, the invention provides method of preparing 2-cyclopropyl amino nicotinic acid (2-CAN). The methods comprise steps of i) reacting, at a temperature of at least 140 °C under pressure, a reaction mixture comprising one equivalent of 2-chloronicotinonitrile, one equivalent of cyclopropylamine (CPA) and a solvent to form 2-cyclopropylamine

nicotinonitrile; ii) adjusting the pH of the reaction mixture to at least 14; and iii) heating the reaction mixture to a temperature of at least 80 °C under reflux conditions for a period of time sufficient to form the 2-CAN. In some aspects, the methods comprise steps of cooling the reaction mixture and adjusting the pH to 6 to precipitate the 2-CAN. In other aspects, the methods comprise a step of isolating the 2-CAN. In further aspects, the pressure is about 60 psi. In yet further aspects, the solvent comprises one or more of trimethylamine, isopropyl alcohol and ¾0.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1. Nevirapine.

Figure 2A-D. Analyses of nevirapine. A, HPLC of batch SA-1 -20; B, HPLC of batch SA-1-21 ; HPLC of batch SA-1-24; D, UPLC 3-D plot of batch SA-1-20.

DETAILED DESCRIPTION

The new method of synthesizing nevirapine (NVP) that is described herein utilizes cyclopropylaminonicotinate esterified at the 2 position and 2-chloro-3-amino-4-picoline (CAPIC) as starting materials. Briefly, the new synthesis process entails two reaction steps (formation of C YCLOR followed by its cyclization) which are carried out in a single solvent system and thus can be performed as one unit operation. By using a common solvent throughout, costly solvent exchanges that otherwise add significant process complexity e.g. requiring waste treatment, remediation, etc., are avoided. In addition, solvent components can be readily recovered and recycled.

After a final purification process, the overall yield for the new process is 86% with an average yield per step of 93%, representing a major improvement over the current commercial methods. Data presented herein shows that, after a final purification step, the solid state properties of the Active Pharmaceutical Ingredient (API), including crystal morphology, particle size distribution and bioavailability, are reproduced in the product that is manufactured by this new method, and the API meets or exceeds all US Pharmacopeia standards. In addition, the nevirapine produced by this process was tested for purity by LC/MS. The results showed that there were no measurable new impurities.

Entailed in the nevirapine synthetic methods described herein are new synthetic methods for producing several starting materials and/or intermediates of the process, e.g. CYCLOR and CAPIC and, in some aspects, 2-CAN and Me-CAN.

PRODUCTION OF NEVIRAPINE (NVP)

1. Synthesis of CYCLOR

As described herein, the first step of the nevirapine synthetic process is the preparation of 2-(cyclopropylamino) nicotinamido-3 ^' -amino-2'-chloro-4 ^' -methylpyridine (CYCLOR) by a novel reaction illustrated in generic Scheme 1 below. In this new method,

2-chloro-3-amino-4-picoline (CAPIC, a new synthesis method for which is also described herein) and a cyclopropylaminonicotinate (CAN) ester, are reacted under basic conditions in a suitable solvent,

CAPIC Ester CYCLOR

Scheme 1 In Scheme 1 , Rl = is a primary, secondary or tertiary ester of a straight chain or branched alkyl group containing from about 1 to about 10 carbon atoms, i.e. about 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. In one aspect described herein, Rl is methyl and the ester is Me-CAN (a new synthetic pathway for production of Me-CAN is also disclosed herein).

In Scheme 1 , the ester is reacted with CAPIC under basic conditions in the presence of one of three types of reagents: 1) R ₂ HMDS, where HMDS refers to either of two related reagents hexamethyldisilazane ([(CH3)3Si]2NH or hexamethyldisiloxane

(0[Si(CH3)3]2)bis(2-methoxyethyl) ether and R ₂ equivalents include but are not limited to, for example, Na, Li, K, etc,; or 2) an alkali metal including but not limited to: NaH, LiH, H, etc; or 3) a base including but not limited to: diazabicycloundecene (DBU). lithium

diisopropylamide (LDA), carbonate, bicarbonate, etc. Optionally, two or more of these reagents may also be present. In some aspects, the preferred base is NaH.

The reaction in Scheme 1 is carried out in the presence of a solvent. Exemplary solvents that may be used include but are not limited to: diglyme, monoglyme, toluene, and other organic solvents including but not limited to, for example, high boiling ethers. "Diglyme" refers to the dimethyl ether of diethylene glycol and "monoglyme" refers to the methyl ether of diethylene glycol. In some aspects, diglyme is the preferred solvent.

The temperature range for performing the reaction depicted in Scheme 1 is from about 50 to about 75 °C, and is preferably from about 60 to about 65 °C.

2. Ring Closure

To produce nevirapine from the CYCLOR, produced by the reaction shown above in Scheme 1 , a solution of CYCLOR in a suitable solvent is heated in the presence of a suitable base to effect ring closure and produce crude nevirapine in quantitative yield, as shown in Scheme 2.

Scheme 2

Suitable bases for this cyclization reaction include but are not limited to: Na, Li, K, ; or 2) an alkali metal including but not limited to: NaH, LiH, KH or 3) a base including but not limited to: NaHMDS, LiHMDS and 4) a base including but not limited to

diazabicycloundecene (DBU), lithium diisopropylamide (LDA), carbonate, bicarbonate, etc.

Exemplary solvents that may be used in the reaction of Scheme 2 include but are not limited to: diglyme, monoglyme, toluene, and other organic solvents including but not limited to various high boiling ethers.

The temperature range for performing the reaction depicted in Scheme 2 is from about 100 to about 120 °C, and is preferably in the range of from about 105-1 17 °C.

In preferred aspects of the invention, the base and solvent that are used during ring closure are the same as those used during CYCLOR formation, thus significantly simplifying and streamlining the synthesis procedure and reducing costs. In this aspect, the reactions of Schemes 1 and 2 may even be earned out in the same container by adding additional reagents as needed and increasing the temperature. However, generally the solution comprising CYCLOR that is obtained after reaction 1 is transferred to a new reaction container.

Nevertheless, isolation of the intermediate CYCLOR is generally not required. In addition, it is generally possible to recover the solvents that are employed (e.g. by distillation) and to reuse them in the same or in different reactions.

Production of crude nevirapine as illustrated in Scheme 2 may be followed by isolation and/or purification of the nevirapine via techniques that are known in the art, e.g. by precipitation, filtering, washing, drying, etc., as needed. More details of these procedures are shown in the Examples section below.

In one aspect of the invention, the CAN ester that is employed in the synthesis of NVP is Me-CAN. An exemplary reaction of this type is shown below in Scheme 3. In some aspects, the base that is employed is NaH and the solvent is diglyme. Yield of NVP under these conditions is 90-100%, as measured by high performance liquid cliromatography (HPLC) and ultra-performance liquid chromatography (UPLC). This embodiment is illustrated in Scheme 3 below:

Scheme 3

PRODUCTION OF STARTING MATERIAL CAPIC

In some aspects of the present novel NVP synthesis methods, the starting material CAPIC is synthesized via a novel method that is illustrated in Scheme 4. The new CAPIC process entails five reaction steps in which the first three are "telescoped" (condensed or linked) into a single process to produce the intermediate 2-chloro-3-cyano-4-picoline (CYCIC) using inexpensive starting materials. The conversion of CYCIC to CAPIC is carried out under the same conditions as those employed by known manufacturing processes (see Scheme 5).

New CAPIC Process

Ylidene r.t. Enamine

(85%) CYCIC (isolated) (96%) COMAD (97%) CAPIC

Overall Yield 79%

Scheme 4 Commercial Process currently used for synthesizing CAPIC (for comparison)

POCI-

Scheme 5

The process of Scheme 4 was initially developed using commercially produced dimethylformamide dimethyl acetal (DMF-DMA) in Step I B. A cost analysis showed that commercial DMF-DMA was by far the most significant cost driver in this process route, and so an alternative was researched, using an on-site preparation of the dimethylformamide dimethyl sulfate adduct (DMF-DMS). Indeed this adduct works at least as well as the commercial DMF-DMA in the chemistry of Step IB, and reduces the cost of CAPIC synthesis to only a fraction of that is incurred when commercial DMF-DMA is used.

The first step of the 3 -step "telescoped" reaction (referred to herein as Step 1 A) is carried out as follows: malononitrile is combined with acetone in a suitable solvent (e.g. toluene) and in the presence of a catalyst (e.g. aluminum oxide, piperidinium acetate, etc.) and reacted at about 20°C or lower (e.g. about 15-20°C) for a period of time sufficient to permit the formation of the ylidene: alkylidene-malononitrile, e.g. for about 15 minutes to about 1 hour, e.g. about 20-3- minutes.

For the second step (Step I B), after removal of the catalyst the filtrate containing the ylidene is reacted (under N ₂ ) with dimethylformamide dimethylacetal (DMF-DMA) and/or dimethyformamide dimethylsulfate adduct (DMF-DMS) which is prepared in situ in the presence of acetic anhydride to form the corresponding enamine. The role of DMF-DMA and DMF-DMS is formylation of active methylene groups to give enamines, i.e. they act as a Vilsmeier reagent and other Vilsmeier reagents might also be employed. The reaction is carried out at a temperature of from about 40-55°C, preferably from about 45-50 °C, for a period of time ranging from about 1 -4 hours, e.g. for about 2 hours.

To effect ring closure and chlorination of the enamine to produce CYCIC (the third step, Step 1C, of the telescoped 3-step synthesis), the solution (still using the same solvent type used in steps 1A and IB, e.g. toluene) is acidified and a chlorinating agent is added, resulting in a Pinner reaction which effects ring closure and formation of

2-chloro-3-cyano-4-methyl pyridine (CYCIC). This may be brought about by reaction with, for example HCl and acetic anhydride, or acetic acid. Step 1C of the synthesis reaction is also advantageously earned out using the solvent that was used for steps 1 A andlB, e.g. toluene. A schematic of these three steps "telescoped" into one reaction is shown below. The product CYCIC is isolated for further processing as described below, e.g. to form CAPIC, or for any other purpose. The isolated CYCIC yield is 85% over these three telescoped steps which use a common solvent, e.g. toluene.

Telescope of first three steps into one to produce CYCIC

Ylidene 1 B

1A

HCI(g) Step IC

Overall Yield 85%

IC

2-chloro-3-cyano-4-picoline (CYCIC) CYCIC produced as described above is placed in a different solvent system, e.g. a suitable acidic/ aqueous solvent system to perform step 2 of the 3 step reaction shown in Scheme 4 above, and shown separately below. Briefly, hydrolysis is carried out e.g. using a combination of a strong acid such as sulfuric acid or aqueous HC1 and a strong base is used such as NaOH or KOH to isolate 2-chloro-3-amido-4-methyl pyridine (COMAD).

COMAD is in turn isolated and a Hoffman rearrangement is performed as shown in step 3 of Scheme 4, and as shown separately below, to convert the COMAD to the product CAPIC, which can be isolated and used for any suitable purpose. Briefly, a halogenating agent (such as e.g. NOBr, NaOCl or another brominating agent such as N-bromosuccinimide (NBS)) is added to an aqueous solution of COMAD at e.g. from about 0-5°C for from about 10 to 30 minutes, allowing the temperature of the reaction mixture to rise to about e.g. 20-25 °C as the exothermic reaction proceeds, e.g. for about 1 -2 hours. The product CAPIC is then recovered by extraction in a suitable solvent, e.g. toluene, and dried, providing the isolated product for use in other reactions. In one aspect, CAPIC is used as a starting material for the synthesis of NVP.

The overall yield for the new CAPIC synthetic process shown in Scheme 4 is 79%, with an average yield per step of 95%. As noted, the identification of the inexpensive common solvent (toluene) facilitated the consolidation of the first three reactions into a single unit operation. In doing so, costly solvent losses that require waste treatment, remediation or recycling were avoided. At the conclusion of the reaction, approximately 75% of the toluene is advantageously recovered and recycled (reused) as part of the process. The final two steps are carried out in aqueous media in virtually quantitative yield. A major advantage of this process is the discovery that an in situ preparation of DMF-DMS adduct can be successfully used in step I B.

PRODUCTION OF STARTING MATERIAL Me-CAN AND ITS PRECURSOR 2-CAN

The exemplary NVP building block, Me-CAN, has heretofore been very expensive to obtain, driving up the overall cost of the product NVP. The current commercial preparation of one of the building blocks, 2- cyclopropylamino nicotinic acid (2-CAN), is a two-step process. The first step is the formation of 2-cyclopropylamino nicotinonitrile from 2-chloronicotinonitrile. The process requires approximately 4 equivalents of cyclopropylamine (CPA) which is a major cost driver for this method. The isolated product from this reaction is then subjected to hydrolysis conditions in which the nitrile is converted to the corresponding acid using aqueous alcoholic potassium hydroxide at reflux temperature. The 2-cycloproylamino nicotinic acid (2-CAN) is isolated as a zwittern ion. The overall yield of this two-step prior art process, illustrated in Scheme 5 below, is 70%.

Scheme 5

Described herein is a new method of producing Me-CAN that provides significant cost improvements over prior art methods (see Scheme 6 below). For example, in some aspects, the first two steps of the prior art process have been consolidated into a single unit operation which provides much higher yields (91 % versus 70%).

Scheme 6

Briefly, the starting material 2-chloronicotinonitrile is reacted with cyclopropylamine (CPA) to form 2-cyclopropylamine nicotinonitrile. However, by running this step of the reaction at higher temperature and under pressure, the amount of CPA that is used was reduced from 4 equivalents to 1 equivalent, which represents a major cost benefit. In the new method, the reaction mixture is then heated to reflux with the addition of KOH to hydrolyze the 2-cyclopropylamine nicotinonitrile, thereby forming 2-CAN. The 2-CAN is then converted to the methyl ester by treatment with thionyl chloride to generate the corresponding acid chloride (not shown in Scheme 6), which is then quenched with methanol to produce the methyl ester of 2-CAN (i.e. Me-CAN) in 95% yield. The overall yield of this new process to produce methyl ester of 2-CAN in a two-step process is 86%. Details of an exemplary reaction as illustrated in Scheme 6 are provided in the Examples section below. Me-CAN synthesized by this method was use tested to prepare nevirapine and no detectable impurities were observed in the API product by HPLC/MS.

In general, as illustrated in Scheme 6, Step 1A of the synthesis is carried out in the presence of a suitable solvent system, e.g. comprising triethylamine (Et ₃ N as shown, also referred to as TEA), isopropyl alcohol (IPA in Scheme 6) and H ₂ 0 in a ratio of 1.3 : 1. However, this solvent system may be varied, for example, methyl alcohol, propyl alcohol, ethyl alcohol, and other alcohols may also be used for Step 1A.

Step 1A is typically carried out at a temperature in the range of from about 120 °C to about 150 °C, and is usually carried out at about 140 °C, for a period of time ranging from about 6 hours to about 12 hours, preferably for at least about 6 hours. Further, this reaction step is generally performed under pressure. The reagent is placed into vessel and pressurized using N ₂ to about 10 psi, following which the reaction mixture is heated, which generates additional pressure to about 60psi.

Step IB of the reaction is carried out in the presence of a suitable solvent system, e.g. IPA and H ₂ 0 in a ratio of about 1.3 : 1. However, this solvent system may also be varied, for example, methyl alcohol, propyl alcohol, ethyl alcohol, and other alcohols may also be used for Step IB. A strong base (e.g. KOH as shown, or NaOH, etc.) in an amount sufficient to bring the pH of the solution into the range of from about 12 to about 14, and preferably to about 14, is added and the reaction is allowed to proceed for a period of time ranging from about 6 hours to about 15 hours, preferably at least aboutl2 hours.

Thus far in the reaction, the product that is formed is 2-CAN, which is isolated e.g. by precipitation, filtration, drying, further purification, etc., as needed. This synthetic pathway for forming 2-CAN is, in and of itself, a novel reaction and in some aspects, the desired product is 2-CAN. In other words, the synthesis can be stopped after Step IB and the 2-CAN need not undergo further reaction, i.e. need not be converted to the methyl ester as shown in Scheme 6, but may be used for another purpose. For example, esters other than the methyl ester may be formed, e.g. ethyl alcohol, propyl alcohol, butyl alcohol and other alcohols may be used to produce the corresponding ester. Other possible uses of the 2-CAN include but are not limited to, for example, its use to prepare nevirapine using a different overall synthetic pathway

If the desired end product of the reaction is Me-CAN, the isolated 2-CAN is further reacted with an agent that generates the corresponding acid chloride. Exemplary agents include but are not limited to: thionyl chloride, or oxalyl chloride in the presence of DMF, or via a Friedel-Crafts reaction, or by using any other acylating agent. The reaction mixture is heated (e.g. to a temperature in the range of from about 30 °C to about 60 °C, and preferably to about 50°C) and the reaction is allowed to proceed under reflux conditions (i.e. with an attached condenser to prevent reagents from escaping) for a period of time ranging from about 20 minutes to about 2 hours, and preferably about 1 hour. The reaction is then quenched with a methyl source (e.g. methanol) to produce the methyl ester of 2-CAN (i.e. Me-CAN), which is isolated, e.g. by work up, washing, etc. as needed to insure purity. At any stage of the reactions described herein, the progress of a reaction or a step of a reaction may be checked, for example, by subjecting a sample of the reaction mixture to an analytical technique such as HPLC, UPLC, various types of chromatography, mass spec, etc. or other suitable techniques. The isolated Me-CAN is, in some aspects, used in the production of NVP as described herein.

Those of skill in the art will recognize that the reactions disclosed herein have been performed largely on a laboratory scale, but can be readily converted to industrial scale syntheses carried out in large commercial operations.

Before exemplary embodiments of the present invention are described in greater detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

Where a range of values is provided, it is understood that each intervening value between the upper and lower limit of that range (to a tenth of the unit of the lower limit) is included in the range and encompassed within the invention, unless the context or description clearly dictates otherwise. In addition, smaller ranges between any two values in the range are encompassed, unless the context or description clearly indicates otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Representative illustrative methods and materials are herein described; methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference, and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such

publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual dates of public availability and may need to be independently confirmed.

It is noted that, as used herein and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as support for the recitation in the claims of such exclusive terminology as "solely," "only" and the like in connection with the recitation of claim elements, or use of a "negative" limitations, such as "wherein [a particular feature or element] is absent", or "except for [a particular feature or element]", or "wherein [a particular feature or element] is not present (included, etc.)...".

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

EXAMPLES

EXAMPLE 1. Preparation of Nevirapine: Exemplary synthesis

(Crude)

Scheme 7

Step I A: CYCLOR Formation

A 500 ml 3 -neck round-bottom flask was fitted with an overhead stirrer, a thermocouple and an addition funnel under N _2. The flask was charged with CAPIC (15 g, 105 mmole, 1.0 equiv) and NaH (7.56g, 189 mmole, 1.8 equiv), followed by diglyme (75 ml, 5ml/g of CAPIC). The mixture was stirred while heating to 30 °C, then held at 30 - 35 °C for 30 minutes, upon which gradual evolution of ¾ gas was observed. The temperature of the mixture was increased to 60 °C over a time period of about 3 hours. The reaction was held constant until the evolution of H ₂ gas had subsided, e.g. 20-30 minutes. A separate 150 mL, 3 necked flask, purged with N ₂ , was charged with Me-CAN (21.19 g, 192.2 mmol, 1.05 equiv) and diglyme (22.5 ml, lml/g) and the mixture was heated to ~55°C. The solution of Me-CAN was slowly transferred to the suspension of CAPIC anion while maintaining the temperature of the CAPIC mixture at 60 - 65 °C. The charge line was rinsed of Me-CAN with 5 ml of diglyme. The resulting reaction mixture was held at 60-65 °C for about 2 hours, and then assayed for reaction completion e.g. by HPLC or UPLC. After the reaction was complete, the reaction mixture was heated to 80 °C and held at this temperature until used in the next step (I B).

Step IB: Synthesis of Crude Nevirapine

A 250 mL, 3 -neck flask, with an overhead stirrer, a thermocouple and an addition funnel purged with N ₂ was prepared, charged with NaH (7.14 g, 178.5 mmol, and 1.7 equiv) and diglyme (22.5 ml), and the suspension was heated to 105 °C. The reaction mixture containing CYCLOR (from Step 1A) was slowly transferred into the NaH suspension over a period of 30 minutes, while keeping the temperature of the mixture at 100 - 1 10 °C. The charge line was rinsed of CYCLOR with 5 ml diglyme. After the addition of CYCLOR was complete, the reaction mixture was held at 100 - 125 °C for about 2 hours, then assayed for reaction completion, e.g. by HPLC or UPLC. The mixture was cooled to 0-5°C. The excess sodium hydride was slowly quenched by the addition of 30 mL of water, while keeping the temperature below 50 °C. After quenching was complete, 60 - 70 ml of diglyme/water was distilled off from the reaction mixture under reduced pressure at 70 - 80 °C. 125 ml of water was added with stirring to ensure that all salt was dissolved. 51 ml of cyclohexane and 15 ml of ethanol were added while stirring and the pH of the mixture was adjusted to 6 - 8 by the addition of glacial acetic acid (19.5 g, 3.09 mmol), upon which nevirapine precipitates as a solid. The suspension was cooled to 0 -10°C, and stirred for about one hour, during which time additional nevirapine precipitated. The product was isolated by vacuum filtration, and washed successively with water (3x30ml) and a 20% ethanol: water (2x20ml) mixture. The product was dried at 90-1 10°C under vacuum to a constant weight. In one preparation, the dried weight of crude nevirapine was 25.4 g (91 %).

Step 2: Preparation of Pure Nevirapine

Purified

Scheme 8

Procedure:

Nevirapine crude (20g, 75.1 mmol) and purified water (86 mL) were added to a 500 ml 3-neck round-bottom flask fitted with magnetic stirrer, thermocouple and addition funnel. The mixture was stirred at room temperature to dissolve the nevirapine and then the solution temperature was lowered to 0-5°C using an ice/water bath. Cone. aq. HCl (23.2 mL, 277.6 mmol) was added dropwise to the above slurry while keeping temperature below 5°C. After HCl addition was completed, the reaction mixture was stirred for about 30 minutes at 0-5°C to make sure all nevirapine had dissolved. Activated carbon (0.6 g) was added and the mixture was stirred for at least another 30 minutes while keeping the temperature at 0-5 °C. The solution was filtered using a celite pad to capture the carbon. The celite pad was rinsed with 2x 10 mL water and the filtrate was re-filtered using a 4 μιτι filter to remove any insoluble material/fibers, etc. , before moving to next step to precipitate the final product.

The clarified filtrate was transferred to a 500 mL 3-neck flask fitted with a magnetic stirrer, thermocouple and an addition funnel. The solution was cooled to 0-5 °C and about 10 ml NaOH (50% solution) was added drop-wise to achieve a pH between 4 and 7, while keeping temperature below 5 °C. A white precipitate appeared when the desired pH was reached. The mixture was stirred for about 30 minutes and the precipitated product was isolated by vacuum filtration, washing the solid with 3x20ml water. The wet cake was dried at 90 -1 10°C under vacuum to a constant weight. In an exemplary synthesis, the isolated yield was 19.2g (96%) and the purity was 100% by HPLC.

A Process Flow Diagram for this procedure is depicted in Figure 2. A typical overall yield for the synthesis was 87%. EXAMPLE 2. Synthesis of the building block CAPIC

Process Chemistry:

The new CAPIC process entails three reaction steps in which the first three are telescoped into a single process to produce 2-chloro-3-cyano-4-picoline (CYCIC) using very inexpensive commodity starting materials. CYCIC is a common intermediate in the previous process and the conversion of CYCIC to CAPIC is carried out under virtually identical conditions. The new CAPIC process chemistry is provided in Scheme 9.

New CAPIC Process

(85%) CYCIC (isolated) (96%) COMAD (97%) CAPIC

Overall Yield 79%

Scheme 9

The overall yield for the new CAPC synthetic process is 77%, with an average yield per step of 95%. Significantly, an inexpensive common solvent (toluene PhMe) was identified for the first three steps; making possible consolidation of these reactions into a single unit operation. In doing so, costly solvent losses that require waste treatment, remediation or recycling were avoided. Approximately 75% of the toluene was recovered and recycled as part of the process. The final two steps were carried out in aqueous media in virtually quantitative yield.

Experimental Procedures:

Preparation of CYCIC:

Telescoped Process of CYCIC Synthesis r.t

Enamine

Ylidene 1 B

1A

HCI(g) Step IC

Overall Yield 85%

IC

2-chloro-3-cyano-4-picoline (CYCIC)

Scheme 10

Table 1. Reactants for Synthesis of Ylidene: STEP- 1A.

EXEMPLARY PROCEDURE FOR STEP- 1A:

1. A 1 liter 3 -neck round-bottom flask fitted with overhead stirrer, thermocouple, addition funnel and padded under N ₂ was charged aluminum oxide (183 g, 1.8 mole, 1.2 equiv).

2. Malononitrile (100 g, 1.51 mole, 1 equiv) was added to the reaction mixture.

3. Anhydrous toluene (600 niL) was added and the mixture was stirred for 20-30 minutes at room temperature.

4. The reaction mixture was cooled to 20°C. 5. Acetone (1 1 1 mL, 1.51 mole, 1 equiv) was added to the above reaction vessel while keeping temperature at or below 20°C.

6. The reactor contents were stirred at room temperature (20°C) for 2 hrs.

7. The aluminum oxide was then filtered off by vacuum filtration and washed with anhydrous toluene (2x25 mL).

8. This filtrate comprising the product alkylidiene-malononitrile was used directly in the next step I B.

Table 2. Reactants for Preparation of Enamine STEP-

EXEMPLARY PROCEDURE FOR ENAMINE SYNTHESIS using DMF-DMS: STEP- I B:

1 . To a 100-ml 3 -neck flask, fitted with a magnetic stirrer and thermocouple, a prepared solution of DMF-DMS (49.48 g), acetic anhydride (3.91 mL) and ylidene stock solution in toluene (90 mL) was charged under nitrogen.

2. This biphasic mixture was stirred vigorously to combine, while cooling to 5-10 °C.

3. Triethylamine (Et ₃ N) (34.66 mL) was added drop-wise, while keeping the reaction mixture at 5-15 °C.

4. After addition was complete, the mixture was warmed to about 20 °C and stirred at this temperature for about 2 hrs, while monitoring for reaction completion.

When the reaction was complete, the mixture was used in the next step (Step 1 C). If product isolation was desired, steps 5-8 were followed. 5. Hexanes (100 mL) were charged to the above mixture and the mixture was cooled to 15-20 °C and stirred for about 15 minutes.

6. The supernatant was decanted, step 5 was repeated one more time and the supernatant was decanted. Decanted phases were discarded.

7. Water (100 mL) was charged to the remaining oily suspension and the mixture was stirred at 15-20 °C for about 10 minutes; the mixture turned from an oily suspension to a suspension of solids.

8. The product was isolated by vacuum filtration, and the isolated solid was dried under vacuum (without heating) to a constant weight.

For the described run, the wet cake weight was 43.3 g and the yield of final dried product was 31.3 g (94%). The purity of product by HPLC was ~98A%. The product co-eluted with reference standard and the structure was confirmed by 1 Ή and 1 ^I 3 ^J C NMR.

Preparation of DMF-DMS adduct or iminium salt as reduced-cost alternative to

DMF-DMA used in Step IB:

Iminium salt

Table 3. Reactants for the Preparation of DMF-DMS

EXEMPLARY PROCEDURE FOR SYNTHESIS OF DMF-DMS adduct or Iminium salt:

1. To a 3 -neck 1 -L round bottom flask with magnetic stirrer, heating mantle,

thermometer, under N ₂ , DMF 73.09 g (1 mole) and dimethyl sulfate 126 g (1 mole) were charged and the mixture was stirred at room temperature for 5-10 minutes to mix. The reaction mixture was slowly heated to 60 °C and held at that temperature for 30 minutes.

2. The reaction mixture temperature was slowly increased to 70-80°C and held at that temperature for 4-6 hours.

3. The reaction mixture was cooled to room temperature.

The product formation was confirmed by Ή and ^lj C NMR. The yield was quantitative and purity was about 95%.

EXEMPLARY PROCEDURE FOR SYNTHESIS OF 2-CHLORO-3-CYANO-4-PICOLINE (STEP-1C)

Table 4. Reactants for Preparation of 2-chloro-3-cyano-4-picoline (CYCIC): Step 1 C:

Step 1 C: Pinner Reaction to produce 2-chloro-3-cyano-4-picoline (CYCIC):

1. After enamine formation was complete as above in Step IB, HC1 gas was slowly charged at room temperature while stirring. After charging was completed the reaction mixture was heated to 50-55°C and held until the reaction was complete. Completion was checked by HPLC.

2. If the reaction was not complete, step 1 was repeated. The reaction was typically complete in about 2 hours.

3. After completion of reaction, the reaction mixture was distilled to remove approximately 75% of solvent, followed by the addition of water (150-200ml) to the residue with stirring.

4. The product was filtered and washed with water (3x50ml). 5. The product was dried at around 30-40 C under vacuum to a constant weight. The average telescope yield for the three steps (Steps 1A, I B and 1 C) is 85%. The purity was -98 A% by HPLC.

STEP 2. Preparation of 2-chloro-3-amido-4-picoline (COMAD):

(96%)

1 C

2

COMAD

Table 5. Reactants for Preparation of 2-chloro-3-amido-4-picoline (COMAD): Step 2:

EXEMPLARY PROCEDURE FOR PREPARATION OF 2-chloro-3-amido-4-picoline (COMAD):

1. A 250 mL reactor was fitted with thermocouple, a heating and cooling system and a condenser.

2. The reactor was charged with solid CYCIC (20.0 g).

3. Sulfuric acid (44.99 g) was added at a rate that ensured a content temperature of

40-50°C.

4. After all the sulfuric acid was added, the mixture was agitated for about 15 minutes, allowing the CYCIC to dissolve into the sulfuric acid.

5. The reaction mixture was heated slowly to 105°C over a one hour period. 6. The reaction mixture was held at a temperature of 105°C for 6-7 hours, after which a sample was checked for the completion of hydrolysis by HPLC.

7. The reaction mixture was then cooled to 70-75°C and water (40 g) was added slowly over 30 minutes while maintaining a content temperature at or below 90°C.

8. Water (140 g) was added to the reaction mixture, bring the temperature of the reaction mixture to about 40-50°C.

9. After all the water was added, the reaction mixture was cooled to 10-15°C.

10. NaOH (50%) was charged to the reaction mixture while keeping the temperature below 35°C.

1 1. The pH of the solution was checked after 90% of NaOH was charged and the pH was recorded.

12. The pH of the reaction mixture changed dramatically during the last 10 % charge of NaOH. After all the NaOH is charged the pH should be about 12. If the pH was below 10, additional NaOH was added to bring the pH to 10-12.

13. The white / light yellow solid was filtered through a Buchner funnel using filter paper.

The filtration was done between 30-35°C.

14. The wet cake was washed with warm (30°C) water (3x 20 g) and filter dried to remove liquid.

15. The solid was dried under vacuum (25-30 inch Hg) at between 30-35°C

13. In an exemplary synthesis, the isolated yield was 96.2%. HPLC: Wt. % 98-100% with CYCIC less than 0.1%.

STEP 3. Preparation of 2-choloro-3-amino-4-picoline (CAPIC)

2 (97%) 3

COMAD CAPIC EXEMPLARY PROCEDURE FOR PREPARATION OF 2-choloro-3-amino-4-picoline (CAPIC):

Vessel 1. Preparation of NaOBr solution

1. Water (25 g) was charged into a 3 -neck flask fitted with thermocouple, dropping funnel and cooling system.

2. 50% NaOH ( 19.27g) was added into the reactor.

3. The mixture was cooled to 0-5°C,

4. Br ₂ (10.614 g) was added slowly while maintaining the temperature of the reactor between 0-5°C.

5. The reaction was held for 30 minutes at 0-5°C.

Vessel 2

1. COMAD (10.3 g) was added to a 3-neck flask fitted with a thermocouple, a

dropping funnel, and a heating and cooling system.

2. Water (15 g) was added to the reactor and the suspension was agitated.

3. The mixture was cooled to 0-5°C.

4. The NaOBr solution of vessel # 1 was added to the COMAD suspension in vessel # 2 slowly while maintaining the temperature between 0-5°C.

5. After charging was complete, the temperature of the reaction mixture was held at 0-5°C for 15-20 minutes. A clear yellow solution resulted; no solid or suspension was formed.

6. The reactor contents were allowed to warm to 15°C and were held at this temperature for 15-20 minutes.

7. The reaction mixture was heated to 25°C and maintained at a temperature between 22-25°C for 1.5 hours, or until the evolution of heat subsided.

8. 10 ml of water was added to the reaction mixture which was then heated to 80°C and held for 1 hour.

9. The reaction mixture was then cooled to 50-60°C and toluene (21.62 g) was added; the mixture was agitated for 15-20 minutes.

10. The top organic layer was separated. 1 1. Toluene (10.3 g) was added to the aqueous layer and the mixture was agitated for 15-20 minutes. The agitation was stopped and the top organic layer was separated.

12. The organic layers were combined and washed with water (10 g) and the water layer was decanted.

13. Toluene (25.0 g) was removed via distillation under reduced pressure.

14. The reactor temperature was adjusted to 55-60°C and hexane (6.5 g) was added slowly with agitation over 15 minutes. The solution because cloudy and a white precipitate started to appear.

15. The mixture was cooled slowly to room temperature and then to 0-5°C.

16. The mixture was held at 0-5 °C for 1 hour.

17. The solid precipitate was retrieved by filtered and washed once with hexanes (6.6 g).

18. The product was dried under vacuo at 25°C to a constant weight.

In an exemplary synthesis, the isolated yield was 8.34 g (96.9%) of off white to white crystalline product.

CONCLUSIONS

An ultra-efficient synthetic method has been developed for the synthesis of CAPIC, a strategic building block in the preparation of nevirapine. The new process has the following attributes: high yielding reactions, averaging 95%; inexpensive raw materials; few isolated intermediates; minimal solvent requirements; limited unit operations; and high product purity.

USE OF CAPIC TO MANUFACTURE NEVIRAPINE:

Three batches of CAPIC were prepared using the new process described above. Each batch was then converted to nevirapine using the commercial process shown in Scheme 1 1.

Scheme 1 1. Commercial Nevirapine Process

The chromatographic purity of each nevirapine sample was then measured by HPLC. All three samples were free of any measurable contaminants and were essentially chiOmatographically pure. The individual HPLC chromatograms of the three nevirapine samples are provided in Figure 4A-C. Each of the samples was also subjected to mass spec analysis. The parent peak as well as the fragmentation patterns for each sample was identical to the nevirapine mass spectrum. Separate UPLC analyses of each nevirapine sample were obtained as were 3-D plots of UV/vis. data for the entire chromatogram to demonstrate sample purity. No impurities were detected in any of the three batches using this procedure. An example of the 3-D plot is shown in Figure 4D.

The UPLC and HPLC methods used to determine chromatographic purity is as follows:

UPLC chromatographs were acquired on a Waters Acuity UPLC H-Class system using a Waters BEH C18 column (1.7 μηι, 2.1 mm x 50 mm). A gradient of 5% ACN in H ₂ 0 to 90% ACN in H ₂ 0 was applied from 0.5 min to 9.0 min at a flow rate of 0.6 mL/min, followed by a hold at 90% CAN from 9.0 min to 10.0 min.

HPLC chromatographs were acquired HPLC on an Agilent 1260 Infinity system using an Agilent Poroshell 120 EC-C18 column (2.7 μηι, 4.6 mm x 50 mm). A gradient of 5% ACN in H ₂ 0 to 95% ACN in H ₂ 0 was applied from 0.5 min to 6.5 min at a flow rate of 1 .5 mL/min.

EXAMPLE 3. Synthesis of Me-CAN

Overall Yield 86%

Experimental Procedures: Telescoped process for preparation of 2-CAN Step 1 A: Preparation of 2-cyclopropylamino nicotinonitrile

Stock solution

2-chloronicotinonitrile Cyclopropylamine 2-cyclopropylamino nicotinonitrile

Table 6. Materials for 2-cyclopropylamino nicotinonitrile

EXEMPLARY PROCEDURE:

1. In a 150 ml pressure vessel was charged 2-chloro nicotinonitrile 20.0 g, 144.35 mmole, 1 .0 equiv). cyclopropylamine (10 ml, 144.35 mmole, 1 .0 equiv) and triethylamine (20.1 1 ml, 144.35 mmole, 1.0 equiv).

2. 60 ml H ₂ 0 and 80 ml IPA were added into the reaction mixture.

3. The vessel was pressurized using N ₂ gas to a pressure of 10 psi, following which the reaction mixture was heated to a temperature of -140 °C. The pressure gauge on the vessel indicated a final pressure of 60 psi at 140 °C.

4. The reaction was held at 140 °C temperature for 6 hours and was monitored by HPLC to ensure complete consumption of the starting material 2-chloro nicotinonitrile.

5. After complete consumption of the starting material and the formation of the product, the reaction mixture was cooled to room temperature, depressurized and was taken forward to the next step.

Step IB: Procedure for 2-cyclopropyl amino nicotinic acid (2-CAN)

-cyclopropylamino nicotinonitrile stock solution

Table 7. Materials for 2-CAN synthesis

w/w

EXEMPLARY PROCEDURE:

1. KOH pellets were charged to the reaction mixture containing 2-(cyclopropylamino)-nicotinonitrile in H ₂ 0/IPA mixture with vigorous stirring (-45% KOH solution can also be used). An exothermic increase in temperature from room temperature to 40°C was observed.

2. The temperature of reaction mixture was ramped to 80 °C and was held under reflux for about 12 hours. The progress of the reaction was monitored by HPLC and once the starting material was fully consumed, the mixture was cooled to a temperature of 0 - 5 °C and HC1 (37%) was charged slowly drop-wise to bring the pH of the mixture to about 6, while maintaining temperature below 10 °C.

3. The product 2- cyclopropylamino nicotinic acid (2-CAN) precipitated out as a white solid and was isolated via vacuum filtration. The wet cake was washed with a minimal amount of water and dried at a temperature between 70 - 80°C under vacuum to a constant weight.

4. The isolated yield of 2-CAN was 23.40 g, 91 %.

Step 2: Procedure for Synthesis of Methyl 2-(cyclopropylamino) nicotinate (Me-CAN)

2-CAN Me-CAN

Table 8. Materials for synthesis of Me-CAN

EXEMPLARY PROCEDURE:

1 . A 250 ml 3 -neck flask fitted with addition funnel, thermocouple and stirrer, under N ₂ , was charged with 30 g of 2-CAN (53.45 mmole. 1 equiv.), dry toluene 150 ml. The resulting slurry was agitated at room temperature.

2. The reaction mixture was charged with thionyl chloride (82.66 g/50.5 ml, 69.48

mmole) for five minutes. The reaction mixture exothermed to 40 - 50°C from room temperature.

3. The reaction mixture was stirred at 40 - 50°C for 30 minutes. A sample was then

checked for completion of acid chloride formation by quenching with MeOH and running on HPLC.

4. MeOH (34 ml) was charged drop wise over 5-10 minutes while temperature was kept below 50°C.

5. The reaction mixture was stirred for about 1-2 hours and then checked for completion by HPLC.

6. Once the reaction was complete, excess MeOH was distilled off. The reaction mixture was cooled to 0 -10°C and charged with 100 ml H?0. The pH was adjusted slowly using NaOH (20%) to a pH of ~ 9. The reaction mixture was agitated for about 30 minutes.

7. A phase cut was performed using toluene and the toluene layer was retained. The aqueous layer was extracted once more with toluene (25ml) and the organic (toluene) layers were combined and washed with water (25ml). The aqueous wash was discarded. Toluene was removed under vacuum to achieve a dry product.

8. After drying, the methyl ester of 2-CAN was isolated as a light brown liquid.

9. The isolated yield of 2-CAN methyl ester was 30.75g; 95%.

The UPLC and HPLC methods used to determine chromatographic purity are as follows:

UPLC chromatographs were acquired on a Waters Acuity UPLC H-Class system using a Waters BEH CI 8 column (1.7 μιτι, 2.1 mm x 50 mm). A gradient of 5% ACN in H ₂ 0 to 90% ACN in H ₂ 0 was applied from 0.5 min to 9.0 min at a flow rate of 0.6 mL/min, followed by a hold at 90% CAN from 9.0 min to 10.0 min.

HPLC chromatography were acquired HPLC on an Agilent 1260 Infinity system using an Agilent Poroshell 120 EC-C 18 column (2.7 pm, 4.6 mm x 50 mm). A gradient of 5% ACN in H ₂ 0 to 95% ACN in H ₂ 0 was applied from 0.5 min to 6.5 min at a flow rate of 1.5 mL/min.

While the invention has been described in terms of its several exemplary embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.