Various criteria could be applied to evaluate candidate reactions, subject to the optimisation objectives and data availability. In this work, our objective was to find efficient reaction routes whilst maintaining environmental efficiency. Although many reactions in Reaxys provide attributes such as yield, selectivity and reaction conditions, such information cannot be found from the KEGG dataset or other commonly used biological databases. Therefore, only global criteria determined from the data available in both Reaxys and KEGG databases were used to design the assessment scores. After trials to avoid failure of computation and biases, the global criteria were designed to include atom economy of reaction steps and price of building blocks to consider both route efficiency and operational costs. Of course, changes in global criteria would significantly alter the optimisation results. Here we chose a minimum set of criteria to demonstrate the overall approach.