With the redesign of three chemical steps, the throughput of the valsartan manufacturing process could be significantly increased, and with the substitution of chlorobenzene with cyclohexane in the bromination of 4′-methyl-biphenyl-2-carbonitrile (6) to 4′bromomethyl-biphenyl-2-carbonitrile (5), halogenated solvents are no longer used in the whole valsartan production process. The alkylation of (S)-2-amino-3-methyl-butyric acid benzyl ester (8) with 4′-bromomethyl-biphenyl-2-carbonitrile (5), and the acylation of (S)-2-[(2′-cyano-biphenyl-4-ylmethyl)-amino]-3-methyl-butyric acid benzyl ester (4) to (S)-2-[(2′-cyano-biphenyl-4-ylmethyl)pentanoyl-amino]-3-methyl-butyric acid benzyl ester (3) were thoroughly modified. In the acylation of 4 to 3, N-ethyldiisopropylamine was replaced by aqueous sodium hydroxide by using the conditions of the Schotten-Baumann reaction, leading to a better quality of intermediate 3. In the alkylation of 8 with 5, N-ethyldiisopropylamine was indirectly replaced by aqueous sodium hydroxide. The reaction runs under homogenous conditions with (S)-2-amino-3-methyl-butyric acid benzyl ester (8) acting as acceptor for hydrobromic acid; recycling of 8 is performed by extraction with aqueous sodium hydroxide.

The manufacturing process for lumefantrine, 2, one of the two active principles in the fixed-dose combination of the antimalarial drug Coartem, was reworked. For the conversion of 2-chloro-1-(2,7-dichloro-9H-fluoren-4-yl)ethanone, 5, to 2-dibutylamino-1-(2,7-dichloro-9H-fluoren-4-yl)ethanol, 8, a onepot process was developed that eliminated isolation of the epoxide 2-(2,7-dichloro-9H-fluoren-4-yl)oxirane, 7. Significant increase in throughput was achieved by applying new reaction and crystallization conditions for the Knoevenagel condensation of 2-dibutylamino-1-(2,7-dichloro-9H-fluoren-4-yl)ethanol, 8, to 2-dibutylamino-1-{2,7-dichloro-9-[1-(4-chlorophenyl)meth-(Z)ylidene]-9H-fluoren-4-yl}ethanol, 2.

Artemisinin and its derivatives, such as artemether, are highly sensitive compounds, which require careful optimized production processes for their manufacture. Due to robustness issues, the manufacturing procedure of the reduction of artemisinin with potassium borohydride to dihydroartemisinin was reinvestigated. The most important factor for obtaining optimal yields is to ensure low levels of contamination of potassium hydroxide in potassium borohydride. Application of a lower reaction temperature, fast addition rate of potassium borohydride, and careful control of the pH during the quench with acid are further important parameters in guaranteeing a robust process. In the redesign of the conversion of dihydroartemisinin to artemether, the yield was increased, and dichloromethane was replaced by the ecologically friendlier methyl acetate. A robust manufacturing process for artemether is now at hand, allowing the production of this important medicine reliably and in good quality and yield.

An improved manufacturing process for fluvastatin 1 has been developed by performing the condensation reaction of E-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-2-propenal, 4, with the dianion of tert-butyl acetoacetate and the subsequent low-temperature reduction to 7-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-3,5-dihydroxy-6-heptenoic acid-1,1-dimethylethylester, 2, without isolation of the intermediate 7-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-5-hydroxy-3-oxo-6-heptenoic acid-1,1-dimethylethylester, 3. To be successful, a crucial selectivity problem in the conversion of aldehyde 4 to aldol 3 had to be understood and solved. The improved process allows the omission of two solvents, and the manufacture of fluvastatin at considerably lower cost and in higher throughput.

A novel industrial process for the antiepileptic drug oxcarbazepine 1 has been developed. Unlike the old process, the new process is free from halogenated solvents and can be performed in standard production equipment. It starts from commercially available 1,3-dihydro-1-phenyl-2H-indol-2-one 10. In the key step, an electrophilic ring closure reaction of 2-[(methoxycarbonyl)phenylamino] benzeneacetic acid 5 to 10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine-5-carboxylic acid methyl ester 6 in poly phosphoric acid was applied. For the manufacture of 5, a highly efficient process using a dianion strategy was developed.

It could be argued that opening occurs both from corner-and edge-protonated species, with perhaps the 5 % erythro acetate found in the opening of 1 (the product of nucleophilic retention) arising from the latter intermediate via an open carbonium ion. We think it unlikely that if opening were occurring competitively from both 6 and 8, the stereochemical results would remain constant over such a wide range of solvents and reaction conditions.

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