The Study Of Gabapentin Synthetic Process By A Chemoenzymatic Route

Gabapentin is a key agent for the treatment of epilepsy.Due to its importance,a number of chemical routes have been developed for synthesizing gabapentin.The developed route via the formation of 1-cyanocyclohexaneacetic acid from 1-cyanocyclohexylacetonitrile followed by hydrogenation seems to be a promising approach to afford gabapentin.Unfortunately,the chemical procedure to convert 1-cyanocyclohexylacetonitrile to 1-cyanocyclohexaneacetic acid affords product in low yield and purity due to the low regioselectivity of catalysts.Moreover,the process requires strong acids and bases and considerable amount of organic solvent,thus producing large amounts of waste water.Alternatively,nitrilase-catalyzed hydrolysis of nitriles offers a “greener” protocol with eco-efficiency.However,the reported nitrilases or microorganisms possessing nitrilase activity have the ability to hydrolyze 1-cyanocyclohexylacetonitrile to 1-cyanocyclohexaneacetic acid,the drawbacks including low space-time yield,low substrate loading or poor regioselectivity restricted the industrial applications.Recently,we have constructed a mutant strains(E.coli BL21(DE3)/pET28b(+)-F168V)which produce high activity nitrilase.The thesis focus on the process that convert 1-cyanocyclohexylacetonitrile to 1-cyanocyclohexaneacetic acid by E.coli BL21(DE3)/pET28b(+)-F168 V resting cells,followed by direct hydrogenation to gabapentin.Influences of reaction conditions on nitrilase activity were firstly investigated,followed the scale of reaction system was enlarged to 1L to further evaluate the feasibility of the biocatalytic process for production of 1-cyanocyclohexaneacetic acid for practical application.As a result,hydrolysis of substrate 1-cyanocyclohexylacetonitrile(1.0 M)over a 8 h provided the desired product with a conversion of 92%,representing an outstanding space-time yield of 461 g/L/day,which markedly exceeded the average space-time yield of industrial bioprocess(372 g/L/day).The hydrolytic reactions were carried out at 40°C,150 rpm,13.57 g DCW/L resting cells and 1 M 1-cyanocyclohexylacetonitrile in 1 L purely aqueous solution(initial pH 7.0).The different methods of resting cells conversion solution pretreatment were evaluated.The results indicated that the protein concentration of resting cells conversion solution which was pretreated by aluminum chloride less than 150 ppm and no side effect on hydrogenation catalyst.The hydrogenation conditions of 1-cyanocyclohexaneacetic acid were op-timized by single factor experiments.The optimized conditions were as follows: 10% Raney Ni RTH-4110,1000 rpm and 2 MPa hydrogen.Finally,the thesis compared the two different gabapentin synthetic routes.The optimal route is 1-cyanocyclohexaneacetic acid direct hydrogenation to gabapentin lactam(2-Azaspiro [4.5] decan-3-one),the lactam was then converted to gabapentin by hydrolysis and alkalinization.The optimal hydrogenation of temperature was 110°C.Under the optimal conditions,the highest substrate conversion(>99.5%)and product yield(>95.3%)were obtained at 9 h.The gabapentin lactam was converted to gabapentin by hydrolysis and alkalinization.At this process,the mother liquors were reused in next reaction.The yield of gabapentin from gabapentin lactam was 88.2%.Based on above results,an efficient chemoenzymatic process is devised for synthesizing high-purity gabapentin.The economical of the process make this new pathway suitable for industrial applications.