Psoralen

The PF was purchased from Huanghe TCM market in Lanzhou city (Gansu province) in Northwest China. PF was authenticated by Prof. Zhi-Gang Ma of Pharmacy College of Lanzhou University. Psoralen (PL), IsoPsoralen (IPL), Bavachin (BVC), Neobavaisoflavone (NBIF), Bavachinin (BVCN), Corylin (CRL), Psoralidin (PLD), Bavachalcone (BCL), IBCL and 4MBCL, gentamycin, and clindamycin were obtained from YuanYe Bio-Technology Co., Ltd. (Shanghai, China) and the purities were above 98%. Vancomycin, metronidazole, Colistin, Kanamycin, and the cell viability kit were purchased from Sigma-Aldrich. The strains of C. difficile ATCC 43255 and BAA-1803 were obtained from American Type Culture Collection (ATCC, Manassas, VA, United States). C. difficile strain CICC 22951 was purchased from China Center of Industrial Culture Collection (CICC, Beijing, China). Caco-2 cell was purchased from Shanghai Cell Bank of Chinese Academy of Sciences (Shanghai, China)). Brain heart infusion (BHI) broth and agar were supplied from Guangdong Huankai Microbial Technology Co., LTD (Guangdong, China). Unless otherwise stated, all C. difficile strains were routinely grown in BHI broth or agar at 37°C in anaerobic conditions (85% N₂, 10% H₂, 5% CO₂) in a Forma Anaerobic System (Thermo Scientific™, United States). Stock solutions of all compounds were prepared in DMSO and stored at −20°C.

Standards of psoralen, corylifolin, corylin, bavachinin and chloramphenicol (IS) were purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Standards of neobavaisoflavone, psoralidin, isobavachalcone and corylifol A were purchased from Chengdu Herbpurify Co., Ltd. (Sichuan, China). The purity of all the standards were above 98%, with the chemical structures displayed in Supplementary Fig. S3.
HPLC grade acetonitrile was purchased from Fisher Chemical (USA). LC-MS grade formic acid was purchased from Anaqua Chemicals Supply Inc. (USA). Deionized water was prepared with Molecular Water Purification system. PF were purchased from Bozhou herbal medicine market (Anhui, China) and authenticated by Professor Cheng-Ming Dong and Sui-Qing Chen (Henan University of Chinese Medicine, Zhengzhou, China). Voucher specimens were deposited in Henan University of Chinese Medicine. SPF were processed according to our previous study^{34 (link)}. Briefly, the PF were mixed with 20% (20:100, salt-water, w/v) salt solution (10:1, PF-salt solution, w/v) and placed in a closed container until salt solution was absorbed completely by PF. Then the moistened PF were stir-fried in a metallic pan over a low flame at 130 ± 20 °C for 8.5 min. After cooling, the SPF were dried in vacuum drying oven at 40 °C for 24 h.

Anastrozole (purity >98%), omeprazole (purity >98%) and psoralen (purity >98%) were purchased from Shanghai Yuanye Biotechnology Co., Ltd (Shanghai, China). β-Nicotinamide adenine dinucleotide phosphate (NADP) and lucifer yellow were provided by Sigma (St. Louis, MO, USA). Rat liver microsomes were purchased from BD (Franklin Lakes, NJ, USA). Dulbecco’s modified Eagle’s medium (DMEM) and non-essential amino acid (NEAA) solution were purchased from Thermo Scientific Corp. (Logan, UT, USA). Fetal bovine serum (FBS) was obtained from GIBCO BRL (Grand Island, NY, US). Penicillin G (10,000 U/mL) and streptomycin (10 mg/mL) were purchased from Amresco (Solon, OH, USA). Hanks’ balanced salt solution (HBSS) was purchased from GIBCO (Grand Island, NY, USA). Acetonitrile and methanol were purchased from Fisher Scientific (Fair Lawn, NJ, USA). Ultrapure water was prepared with a Milli-Q water purification system (Millipore, Billerica, MA, USA). All other chemicals were of analytical grade or better.