(a)
(b)
(c)
(d)
(e)
Figure 1: Structure of DKPs known to be produced by the archaeon H. hispanica. (a) Cyclo(D-prolyl-L-tyrosine), (b) cyclo(L-prolyl-L-tyrosine), (c) cyclo(L-prolyl-L-valine), (d) cyclo(L-prolyl-L-phenylalanine), and (e) cyclo(L-prolyl-L-isoleucine).