molecules Article Antiviral Activity of a Cyclic Pro-Pro-β3-HoPhe-Phe Tetrapeptide against HSV-1 and HAdV-5 Ewa Zaczyn´ ska 1 , Krzysztof Kaczmarek 2 , Janusz Zabrocki 2,†, Jolanta Artym 1 and Michał Zimecki 1,* 1 Department of Experimental Therapy, Hirszfeld Institute of ...