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Tuesday, 29 October 2013

Synthesize 7-azanorbornane on an industrial scale

Synthesize 7-azanorbornane on an industrial scale
Patent Number:US 8404865
Title:Process for preparing azabicyclic compounds
Inventor(s):Ambhaikar, Narendra Bhalchandra; Bear, Brian Richard; Fanning, Lev T. D.; Hughes, Robert; Littler, Benjamin
Patent Assignee(s):Vertex Pharmaceuticals Incorporated, USA
Source:U.S. Pat. Appl. Publ., 8pp. CODEN: USXXCO
Abstract:The present invention relates to a process for prepg. azabicyclic compds. that are useful intermediates for synthesizing pharmaceutical compds. or salts thereof.  Thus, azabicyclo[2.2.1]heptane hydrochloride (I·HCl) was prepd. from trans-4-aminocyclohexanol via N-protection with Boc2O in CH2Cl2 contg. Et3N; mesylation with MsCl in CH2Cl2 contg. Et3N; N-deprotection with CF3CO2H; cyclization with aq. NaOH; and treatment with
7-azabicyclo[2.2.1]heptanes are useful intermediates in the synthesis of pharmaceutical compounds and salts thereof. For example, see U.S. Pat. Nos. 6,117,889 and 6,060,473, each of which is hereby incorporated by reference in its entirety
 Despite the title of N. B. Ambhaikar and co-inventors’ patent, “Process for preparing azabicyclic compounds”, it only describes a process for preparing 7-azanorbornane (5) and its HCl salt (6). The inventors state that compound 5 is an intermediate in the synthesis of pharmaceutical compounds, but they do not mention any.

The patent’s examples describe the preparation of 5 and its precursors on a kilogram scale. The first step is protecting the amino group in 1 by converting it to tert-butoxycarbonyl (BOC) derivative 2 with the anhydride (BOC)2O in the presence of Na2CO3. The product is isolated in 88.8% yield. The reaction can also be carried out with K2CO3, but the yield is not reported.
Four-step synthesis of 7-azanorbornane
In the second step, 2 is treated with methanesulfonyl chloride (MsCl) in the presence of Et3N to form methanesulfonate 3 in 96.6% isolated yield. In step three, the BOC group is removed by adding CF3CO2H in two batches. The product is amine salt 4. The recovered salt contains excess CF3CO2H; and as a result, the yield appears to be >100%.
In the final stage, the CF3CO2H salt is treated with NaOH to cyclize it to the desired compound. Azanorbornane 5 is recovered by fractional distillation; treating the fractions with concd HCl gives hydrochloride salt 6. The salt is recovered as a solid, dried, and recrystallized from MeOH and MeOH–THF. Although the examples contain significant detail, the product’s final yield and purity are not reported.
The process is an efficient method for preparing 7-azanorbornane and its salt. It is clearly suitable for large-scale production. (Vertex Pharmaceuticals [Cambridge, MA]. US Patent 8,404,865, March 26, 2013; Keith Turner)
 7-azanorbornane HCl salt (6). 
1HNMR (DMSO-d6) ppm 8.02-8.04 (d); 7.23-7.31 (m); 4.59 (s); 3.31 (s); 2.51-3.3 (m); 1.63-1.75 (m); 1.45-1.62 (m).

In one aspect, the invention includes a process for preparing Compound 7-azanorbornane
Figure US08404865-20130326-C00001
    • or a pharmaceutically acceptable salt thereof, comprising contacting trans-4-aminocyclohexanol with Boc anhydride to produce a compound of formula A
Figure US08404865-20130326-C00002
    • contacting a compound of formula A with methanesulfonic acid to produce a compound of formula B
Figure US08404865-20130326-C00003
    • contacting a compound of formula B with trifluoroacetic acid to produce a compound of formula C
Figure US08404865-20130326-C00004
    • contacting a compound of formula C with hydroxide to produce a compound of formula 
In some embodiments, the invention includes a method of producing a compound of formula 7-azanorbornane Hydrocloride salt
Figure US08404865-20130326-C00005
    • The TFA salt of trans-4-aminocyclohexylmethanesulfonate (200 g, 650.9 mmol) was introduced into a 3-necked flask followed by the addition of water (2.200 L, 11 vol). NaOH (78.11 g, 1.953 mol, 3 eq) was slowly added, keeping the temperature of the reaction mixture below 25° C. and the mixture was stirred overnight. DCM (1.4 L, 7 vol) was then added and the mixture stirred, and the organic layer was separated. The aqueous layer was then extracted a second time with DCM (1.4 L, 7 vol), and the DCM layers were combined. HCl (108.5 mL, 12M, 1.3020 mol, 2 eq) was then added, the mixture was stirred for 30 min and then concentrated on a rotary evaporator to dryness. Acetonitrile (10 vol) was added and the mixture concentrated. This was repeated 3 times until all trace water was azeotropically removed, to provide 7-azabicyclo[2.2.1]heptane hydrochloride. The crude product was recrystallized from acetonitrile (10 vol) to provide 7-azabicyclo[2.2.1]heptane hydrochloride as a colorless crystalline solid.

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