Figure 4. Illustration of molecular fragments.

(A) The structural fragments in neuraminidase (NA) of influenza virus A inhibitors. The molecular structure is divided into 4 fragments according to the substitutes being investigated. The fragments F₁, F₂ and F₃ are three substituent groups, and the fragment F₄ is the remaining part of the molecular parent. (B) In short peptides each side chain of amino acid residue is a fragment.