Volume 278, May 2026, 113237Author links open overlay panel, , Highlights•

[Sb(OH)6]− and gluconate combine to form predominantly one molecular species.

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This primary product is the predominant antimony complex in sodium stibogluconate.

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The nuclear magnetic resonance signals from this predominant species are fully assigned.

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The formation constant for this product from [Sb(OH)6]− and gluconate is 1006 M−1.

Abstract

Sodium stibogluconate is an effective but toxic Sb-containing antileishmanial drug. Despite having been in clinical use for over half a century, the chemical structure of this small-molecule drug remains unknown. Historically, the drug has been thought to comprise an intractable mixture of interconverting species. We report here nuclear magnetic resonance (NMR) spectroscopic experiments that provide the first evidence that the reaction between gluconate and [Sb(OH)6]− produces primarily one molecular species. Multidimensional experiments allow the NMR resonances of this species to be fully assigned. Further experiments on authentic samples and clinical preparations of sodium stibogluconate confirm that the primary product of the reaction of gluconate and [Sb(OH)6]− is the predominant antimony-containing component of the drug. The thermodynamic stability of this predominant species was assessed using a combination of 1H and 121Sb NMR spectroscopic measurements, which afforded a value of K = 1006 M−1 for its formation from gluconate and [Sb(OH)6]−.

Graphical abstractSynopsis: The antileishmanial drug sodium stibogluconate has long been thought to comprise an intractable mixture of species, but nuclear magnetic resonance spectroscopic experiments reveal that the reaction between [Sb(OH)6]− and gluconate, which can be used to prepare the drug, gives rise to a single predominant Sb-containing species.Download: Download high-res image (151KB)Download: Download full-size imageKeywords

Leishmaniasis

Antimony

Pentavalent antimonial

Stibogluconate

Pentostam®

Hexahydroxoantimonate

Data availabilityData are provided within the manuscript or supplementary information files. Raw data sets are available upon request. Crystallographic data for K[Sb(OH)6] and (PPh4)[SbCl6] have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2387910–2387911, and can be obtained from https://www.ccdc.cam.ac.uk/structures/.

© 2026 The Authors. Published by Elsevier Inc.