JPET #90928Supplemental data1/2

Synthesis of 13C-labelled esomeprazole:

[13C6] Aniline (99 atom% 13C) was transformed to [13C6] phenol in 88% yield by diazotation in TFA followed by warming the resulting diazonium salt, according to (1). The reaction proceeded much better in presence of urea (2). Final purification was achieved by flash chromatography.

[13C6] Phenol was methylated with [13C] CH3I (99 atom% 13C) and crushed NaOH in DMSO to give [13C7] anisole in 90% yield. Distillation afforded pure product, which then was converted to [13C7] N-(4-methoxyphenyl)acetamide in 70% yield following published procedure (3). Final purification was performed by crystallization from warm t-butyl methyl ether.

[13C7] N-(4-methoxyphenyl)acetamide was nitrated to afford [13C7] N-(4-methoxy-2-nitrophenyl)acetamide by carefully adding a solution of the substrate in acetic acid to a mixture of nitric acid and water(1:1), keeping the temperature under 20 C for one hour. The mixture was poured onto ice and the formed crystals were recrystallized from a mixture of ethanol and water to give pure product in 83% yield. The [13C7] N-(4-methoxy-2-nitrophenyl)acetamide was hydrolyzed by boiling in 6 M HCl for one hour. After cooling and neutralization, quantitative yield of pure [13C7] 4-methoxy-2-nitroaniline was obtained as beautiful dark orange red crystals.

The [13C7] 4-methoxy-2-nitroaniline was reduced to the corresponding phenylene diamine by catalytic dehydrogenation (10% Pd/C) in 90% ethanol, as easily monitored by the decoloration. To the reaction mixture a slight molar excess of potassium ethyl xanthogenate and KOH was added and the reaction allowed to proceed at 75 C for several hours until complete conversion was obtained according to TLC. The resulting [13C7] 6-methoxy-1H-benzimidazole-2-thiol was isolated after extraction with 0,5 M NaOH from methylene chloride followed by acidification of the water phase with H3PO4 to pH about 6 when the product precipitated out in almost quantitative yield. This labeled mercaptobenzimidazole was then coupled with 2-(chloromethyl)-4-methoxy-3,5-dimethylpyridine as described in (4), using ethanol as solvent and final purification by flash chromatography, to give a 91% yield of [13C7] 5-methoxy-2-([(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]thio)-1H-benzimidazole. Asymmetric oxidation to [13C7] esomeprazole was performed according to (5) with the following deviations. a) The completion of the reaction was followed by TLC (ethyl acetate, methanol, conc. NH4OH and water (60:12:5:5) where Rf for the sulfide, sulfoxide and sulfone are approx. 0.9, 0.6 and 0.55 respectively). b) The potassium salt of the product was directly precipitated from the toluene solution by addition of 1.4 equivalents of potassium methoxide as a concentrated methanol solution, at ambient temperature. c) From the isolated white salt, dissolved in water, the neutral form was obtained by the addition of NH4Cl, extraction with methylene chloride followed by evaporation. d) A second precipitation as potassium salt from a toluene solution of the neutral form, as described above, afforded pure product with an enantiomeric excess of 98%.

REFERENCES

(1) M.R. Pettit, M. Stacey, J.C. Tatlow, J. Chem. Soc. (1953) 3081-3084

(2) Houben-Weyl, Bd VI/1 s. 249 ff

(3) T. Cablewski, P.A. Gurr, K.D. Raner, C.R. Strauss, J. Org. Chem. 59 (1994) 5814-5817

(4) EP 074341 B1 (priority date: August 13, 1981)

(5) H. Cotton, T. Elebring, M. Larsson, L. Li, H. Sörensen, S. von Unge, Tetrahedron: Asymmetry 11 (2000) 3819-3825