Title: back-up compound
Long Title: IUPAC Gold Book - back-up compound
DOI: 10.1351/goldbook.12623
Status: current

Definition
Molecule selected as a replacement for the lead drug candidate should this subsequently fail during further preclinical evaluation or in clinical studies.

Note
Ideally, a back-up should be pharmacologically equivalent to the lead drug but have significant structural differences. Possession of a distinct core scaffold is optimal.

Related Term
- scaffold: https://goldbook.iupac.org//terms/view/12724

Source
- PAC, 2013, 85, 1725. 'Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)' on page 1728 (https://doi.org/10.1351/PAC-REC-12-11-23)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12623/html
- json: https://goldbook.iupac.org/terms/view/12623/json
- xml: https://goldbook.iupac.org/terms/view/12623/xml

Citation: Citation: 'back-up compound' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.12623
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-07-26T07:00:23+00:00