A novel and practical synthesis of mavorixafor (1) is reported. The novelty of this synthetic route is the use of 8chloro-5,6,7,8-tetrahydroquinoline (9) and 1,4-diaminobutane as the materials, instead of 8-amino-5,6,7,8-tetrahydroquinoline (4) and N,N-diprotected aminobutyraldehyde (6a or 6b). The preparation of (S)-8-(4-aminobutylamino)-5,6,7,8-tetrahydroquinoline (13) by resolution with N-acetyl-L-leucine was first achieved. Then the one-pot synthesis of 1 from 13 involving protection, condensation, and subsequent hydrolysis was successfully developed. In addition, the final product with a satisfactory purity (>99.5%, detected by both achiral and chiral HPLC) was obtained by a simple operation (salification) without column chromatographic purification.

The synthesis and characterization of compounds 7c and 8d, the 4(R)‐epimer impurities of zanamivir and laninamivir octanoate, were reported for the first time. Their structures were confirmed by NMR and MS and distinguished from their corresponding active pharmaceutical ingredient (API) by coupling constant in 1H NMR and HPLC spectra. This work is of great significance for the drug‐related substances analysis in zanamivir and laninamivir octanoate.

A series of mono- or bis-quaternary ammonium salts derived from cinchonidine or quinine was synthesized and screened as potent phase-transfer catalysts for the reaction of aza-Michael cyclization, the key step in the synthesis of letermovir. During the reaction of aza-Michael cyclization, the screened monoquaternary ammonium salt quinine derivative Q1 transferred 7 to 8 with 91.9% yield and 58% ee. The application of Q1 was preferred, due to its enantioselectivity, the possibility of reuse, and the lower cost in large-scale preparation. Furthermore, the racemization condition of letermovir enantiomer was also explored for the possibility to develop the resolution/racemization process. With the optimal catalyst Q1 in hand, the synthesis of letermovir may be more convenient and economical in the future.

No abstract