The invention relates to a new family of compounds of the type 2,3-dihydroquinazolin-4(1H)-one and the use thereof as inhibitors of the toxic effects of intracellular-acting toxins, such as ricin, Shiga toxins or the cholera toxin, using retrograde transport to intoxicate the cells, or viruses or bacteria using retrograde and/or syntaxin 5-dependent transport to infect the cells, specifically viruses or bacteria entering into the cells by means of endocytosis, or intracellular parasites.