1 23 Journal of Molecular Modeling Computational Chemistry - Life Science - Advanced Materials - New Methods ISSN 1610-2940 Volume 20 Number 1 J Mol Model (2014) 20:1-13 DOI 10.1007/s00894-014-2069-z How “drug-like” are naturally occurring anti-cancer compounds? Fidele Ntie-Kang, Lydia L. Lifongo, Philip N. Judson, Wolfgang Sippl & Simon M. N. Efange