Cyclo(L-Ala–L-Pro) and cyclo(L-Val–L-Pro) are widely found as natural products in a number of organisms such as bacteria, fungi and plants as well as foods and drinks,including coffee and beer (Pickenhagen et al., 1975; van der Greef et al., 1987; Trigos et al., 1996; Holden et al., 1999; Wang et al., 2010).