Crystal Structure of Sinigrin

Abstract

SINIGRIN is a crystalline thioglucoside, extracted first by Bussy¹ from the seeds of black mustard. It is the potassium salt of the anion [C₁₀H₁₆O₉NS₂]⁻, also called the myronate ion, and the crystals contain one molecule of water per potassium ion. In 1897 Gadamer² proposed formula (I) for the myronate ion. Schneider and collaborators confirmed the thioglycoside linkage in 1914 (ref. 3) and in 1930 (ref. 4) established that sinigrin and analogous glucosides are 1-β-D-thio-glucosides. Important details of the Gadamer formula I were challenged recently by Ettlinger and Lundeen⁵, who have advanced convincing arguments in favour of structure II, with the sugar in the β-gluco-pyranoside form. While Schultz and Wagner⁶ cast some doubt on II, on the basis of infra-red work, the synthesis by Ettlinger and Lundeen⁷ of the closely related glucotropaeolate ion (allyl replaced by benzyl) strongly affirmed the correctness of II. Ettlinger and Lundeen advanced arguments based on reaction mechanisms that suggest a syn configuration of sulphate and thioglucose relative to the C=N double bond. However, these arguments were inconclusive^8,9. The chemistry of sinigrin and related compounds as well as their biological properties have been reviewed recently¹⁰.