Novel Chiral Drug Recovery and Enantioseparation Method: Hollow Fiber Membrane Extraction and In Situ Coupling of Back-Extraction with Crystallization
Lelin Zeng, Qian Liu, Yi Qin, Kewen Tang, Bart Van der Bruggen
Abstract
A novel method was developed for the recovery and enantioseparation of the active pharmaceutical ingredient (S)-amlodipine from pharmaceutical wastewater: hollow fiber membrane extraction and in situ coupling of back-extraction with crystallization. Amlodipine (AD) was extracted from wastewater (W) into an extraction phase (O1) by a commercial extractant P507 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) and subsequently back-extracted into a stripping phase (O2), in which (S)-amlodipine was preferentially crystallized in situ with a chiral resolving agent (D)-tartaric acid. To establish such a coupling system, n-heptane and dimethylsulfoxide (DMSO) were selected as the solvents of O1 and O2, so O1 can be immiscible with both W and O2, and crystallization can also occur in O2. The acidic extractant P507 was selected to transfer amlodipine from W to O2 because amlodipine is a basic molecule. The hollow fiber membrane module was employed as an extraction contactor to avoid the entrainment of droplets and crystalline powders. The effects of the running time, amlodipine concentration, pH, P507 concentration, flow rate, (D)-tartaric acid concentration, DMSO dosage, number of fibers, and temperature were investigated. An ee(S)-AD of 90.7 ± 1.4% and a yield (Y(S)-AD) of 48.8 ± 2.4% for the crystal product were obtained under optimized conditions. The crystal products were characterized by high-performance liquid chromatography and scanning electron microscopy. In this new technology, all reagents were inexpensive chemicals, and membrane extraction was coupled with crystallization for both high enrichment ability and good enantioseparation ability. This technology has application prospect for the recycling of many high-value chiral drugs.