FRAG
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A FRAG is one of the pre-calculated SUBSTRUCTURE types, and is defined as a fragment obtained when all rotatable bonds are cut. A rotatable bond is defined in the following way: only a single bond (saturated bond) that is not included in any ring substructure can be rotated. Amide bonds are not rotatable as they are known to have an energy barrier that prevents rotation. Two cases that have not yet been considered are where steric hindrance prevents rotation, and where an enzymic reaction helps rotation (such as occurs with cis-trans-isomerases). A bond consisting of one hydrogen atom and one non-hydrogen atom is also excluded. FRAG entries can be searched using Substructure Search option.
Examples: