Phase I metabolism
Together with “hot spot” SoM predictions, MetaSite can also predict the structure of the metabolite(s) formed after the metabolic biotransformation(s).
The procedure produces a full set of metabolite structures based on a number of possible metabolic reactions. The metabolites formed are ranked according to the MetaSite Site of Metabolism predictions, yielding a ranked list of metabolites in conjunction with their monoisotopic mass and lipophilicity values. The lipophilicity values are then used to predict the relative retention time of the metabolites.
The estimated relative retention time (RRT) of the metabolites is based on the hydrophilic/lipophilic balance of each metabolite when compared to the parent substrate.
In the cases where experimental retention times were reported together with the pH of the chromatographic column, a good correlation of the estimated RRT with experimental data has been observed.
The predicted RRT therefore provides valuable information when discriminating between metabolites with equal mass during HPLC separation phase.
The RRT values represent the following quantity:
RRT = (RT(metabolite)-RT(substrate))/RT(substrate).
Metabolites with a retention time higher than that of the substrate are therefore expected to have a positive RRT (and vice versa).
Please also note that the estimated RRT depends on the pH of the chromatographic column. By default, the RRT chart in the MetaSite GUI refers to an acid environment, but RRT values referring a neutral or basic environment are produced as well.