1. Department of Natural Products Chemistry, Key Lab of Chemical Biology (MOE), School of Pharmaceutical Sciences, Shandong University, No. 44 West Wenhua Road, Jinan 250012, P. R. China
2. School of Chemistry and Chemical Engineering, Shandong University, Jinan 250010, P. R. China
3. Vitamin D Research Institute, Shanxi University of Technology, Hanzhong 723000, P. R. China
4. School of Pharmacy, Linyi University, Linyi 276000, P. R. China