2-[3,5-bis(trifluoromethyl)phenyl]-N,2-dimethyl-N-[4-(2-methylphenyl)-6-(4-methylpiperazin-1-yl)pyridin-3-yl]propanamide

Synthesis

The most likely process-scale synthesis of netupitant begins with 6-chloronicotinic acid (185). From 185, a one-pot 1,4-Grignard addition/oxidation reaction, developed to provide an improved route to NK1 receptor antagonists, was employed for direct installation of the C4-o-tolyl substituent. Using this procedure, treatment of 6-chloronicotinic acid (185) with otolyl magnesium chloride and subsequent oxidation with Mn (OAc)2 in THF/AcOH generated the o-tolyl nicotinic acid intermediate 187 in 51% overall yield. From this intermediate, a one-pot amide formation could be realized in high yield by conversion of the acid to the corresponding acyl chloride and addition of NH4OH (95% yield). Chloride displacement with 1-methyl piperazine under heating conditions provided intermediate 189 in 95% yield. Employing Hoffman reaction conditions originally reported by Senanayake,171 rearrangement of amide 189 with NBS/NaOMe/ MeOH enabled formation of carbamate 190 in quantitative yield. Reduction of the carbamate with Red-Al provided the desired mono-methylated amine. To access the final drug target, acylation of the intermediate methyl amine with 2-(3,5-bis(trifluoromethyl) phenyl)-2-methylpropanoyl chloride (191) provided the final drug netupitant (XXII) in 81% yield. In this case, due to the cost of 193, the acid precursor to 191, and starting materials previously reported for generating 191/193, as well as issues with isolation of pure intermediates on scale, a novel route to 191 and 193 was also developed during this synthesis, beginning with the inexpensive and readily available bromide 192. This 2-step synthesis of 193 includes Grignard reagent formation, quenching with acetone to yield the intermediary tertiary alcohol, and subsequent carbonylation (TfOH, H2O, CO then NaOH/H2O) to provide 2-(3,5-bis(trifluoromethyl)-phenyl)-2- methylpropanoic acid 193. Finally, conversion of acid 193 to the acyl chloride with oxalyl chloride in DCM provided the necessary acyl chloride 191 in quantitative yield (86% purity).

Definition

ChEBI: A monocarboxylic acid amide obtained by formal condensation of the carboxy group of 2-[3,5-bis(trifluoromethyl)phenyl]-2-methylpropanoic acid with the secondary amino group of N-methyl-4-(2-methylphenyl)-6-(4-methylpiperazin-1-yl)pyridin 3-amine; an antiemetic used in combination with palonosetron hydrochloride (under the trade name Akynzeo) to treat nausea and vomiting in patients undergoing cancer chemotherapy.