Analogues are drugs that have close structural resemblance and similar effects. For instance one could argue that naproxen (Aleve) is an analog of ibuprofen (Motrin/Advil). Most analogues are designed because true synthetic natural products are hard to make, or are not potent enough.
Definition of several. 1a : separate or distinct from one another federal union of the several statesb (1) : individually owned or controlled : exclusive a several fishery â compare common (2) : of or relating separately to each individual involved a several judgmentc : being separate and distinctive : respective specialists in their several fields.
A species is a category within the classification system. Living things of the same type belong to the same species. For example, humans are one species and dogs are another species. Individuals of the same species can reproduce to make more individuals of the same species. Two individuals belonging to different species cannot normally reproduce together. If they do, their offspring is usually infertile and unable to reproduce.