A scope includes those metabolites which can be synthesized form a specified set of seed compounds. An important biochemical question is how a particular product (the target) can be synthesized with a minimal number of reactions from a given set of substrates. The algorithm presented here is able to calculate a pathway performing the synthesis in a minimal number of consecutive steps. The algorithm works as follows: Starting from the seed, an expansion process is preformed as described above. The number of consecutive synthesis steps necessary to produce the target is already determined by the iteration step in which the target was incorporated. During the process, it is recorded which metabolites enable which reactions and which reactions produce which metabolites. With this information, the synthesis pathway is now assembled in a reverse order starting from the target. The obtained pathways in general are not simply unbranched chains but contain reactions which operate in parallel. There may exist other pathways with a smaller total number of reactions which can perform the same conversion, however none with a smaller number of consecutive steps.

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