1. Xi'an Botanical Garden; Institute of Botany of Shaanxi Province; Xi'an 710061 People's Republic of China
2. Dipartimento di Chimica e Chimica Industriale; Università di Pisa; Pisa Italy
3. Division of Organic Chemistry and Biochemistry; Ruđer Bošković Institute; Zagreb Croatia
4. Shaanxi Key Laboratory of Natural Products & Chemical Biology; College of Science, Northwest A&F University; Yangling 712100 People's Republic of China