Froog Team

Chansu is named for Chán sū (蟾酥), the traditional Chinese medicine preparation derived from toad venom, from which bufalin, a bufadienolide (a class of cardiotonic steroids), is isolated. Chansu is a generic medicinal chemistry engine. Given a natural compound, it grounds the compound in the published literature, maps which regions of the molecule matter for its biological activity and why, and generates citation-backed hypotheses for modifying the compound to correct a specific liability such as toxicity, poor solubility, rapid clearance, or weak potency. This is work that a medicinal chemist currently does by hand, one compound at a time, drawing on literature review and structural precedent from approved drugs. The engine keeps three roles strictly separate. Claude retrieves and reasons over the literature, builds a graded importance map of the molecule, and matches identified liabilities to a curated strategy library. RDKit performs every deterministic calculation (molecular weight, logP, TPSA, Lipinski and Veber flags, similarity to the parent compound) and validates every generated structure before it is shown to the user. The strategy library holds six precedent-backed modification strategies, each tied to an approved drug and a citation, so the engine reasons by analogy rather than invention. Every claim in the output carries a provenance tag, computed, literature-cited, or hypothesis pending wet-lab validation, and the tool declines to propose a strategy when no precedent applies rather than fabricate one. Bufalin is the flagship compound, chosen because it has documented anticancer and antiviral activity, multiple targets, and multiple distinct liabilities, which lets one compound demonstrate the engine's range. To confirm the engine generalizes rather than being built around bufalin specifically, a second compound, ursolic acid (a pentacyclic triterpenoid, PubChem CID 64945, sourced with Claude Science), was added as pure data with no change to the engine code. It passed the full pipeline on a structurally unrelated scaffold, which is the project's core architectural claim: adding a compound should only ever require new data. The interface is a multi-screen Streamlit app with RDKit-rendered 2D and 3D molecule views, substructure highlighting for the importance map, a ranked and scored analog list, a provenance-tagged design memo, and a literature sources panel.