Synthetic and natural guanidine derivatives as antitumor and antimicrobial agents: A review

•Guanidine-containing molecules have high therapeutic value.•The main therapeutic interest is as anticancer and antimicrobial agents.•Anticancer mechanisms are mainly by interaction with DNA.•Antimicrobial mechanisms are mainly by interference with microbial cell membranes.•Guanidine-bearing drugs are undergoing clinical trials for the treatment of COVID-19.