Filtering Rules

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ZINC is loaded from commercial supplier catalogs and annotated databases. We only load molecules we feel will be useful for virtual screening.

  • For commercial compounds, we do not load highly reactive compounds, or compounds over 500 g/mol.
  • For annotated compounds and vendor catalogs of bioactives which are often drugs, metabolites, natural products or natural derivatives, we relax these constraints to allow up to 600g/mol and we allow some reactive functional groups that would otherwise not be considered acceptable for screening.
  • For make-on-demand compounds, we may only load only up to 400 g/mol.
  • Some make-on-demand and agent catalogs are incompletely loaded, deliberately. We need to upgrade our hardware and software first.

Our rules do change as our thinking evolves. The current rules are available in textual and graphical form at If you disagree with choices we have made, we would be happy to discuss them with you in our Forum.

To see the filtering rules in effect in ZINC, please see We filter both at load time and also at subset preparation time. Molecules are not loaded if:

  • They do not pass our load-time filtering criteria
  • An error occurs during processing.

Each filtered-out compound is justified with a reason, available via the vendor page. Every compound in every supplier catalog we load has one of four fates:

  • It loaded and visible in ZINC.
  • It is depleted (not longer available) - and may still be in ZINC, marked depleted. Depleted compounds may not persist for long.
  • It was filtered out and never loaded. These are listed as "filtered out" on the vendor pages.
  • It failed at some stage of processing, and may appear nowhere except in the original vendor catalog.

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