Is the Negative Charge on RNHSO₃^-M⁺ an Essential Requirement for Sulfamate Sweetness?

Abstract

Although many structure-taste studies have been carried out on sulfamate (cyclamate) sweeteners, there are still some unanswered questions-notably whether the sulfamate anion, -NHSO(3)(-), is essential for sweetness in this class of compounds. The literature is contradictory on this point; therefore, 14 sulfamate esters RNHSO(3)R', which contain the sulfamate moiety but without the negative charge, i.e., -NHSO(3)(-), have been synthesized and tasted under standard conditions. Almost all of the esters were found to possess strong sweetness accompanied by bitterness. Because the esters had to be heated in water to 60 degrees C to dissolve them, it was necessary to check for partial hydrolysis to the free sulfamic acids, RNHSO(3)H, since they would be sweet and would invalidate the tasting results if formed. This was done by monitoring (gas-liquid chromatography) the formation of alcohol after heating. Negligible or very low hydrolysis to acid was found for all 14 esters. This work, in addition to answering an important structure-taste question, points the way to the potential use of suitable sulfamate esters as additives in situations where the more usual sodium sulfamate salts are unsuitable, for example, in hydrophobic media.

Structures of artificial sweeteners – cyclamic acid and sodium cyclamate with other cyclamates

“…Later, improved and more sophisticated models were proposed by many authors (see, for example, Tinti & Nofre, 1991;Zalewski & Jasiczak, 1994;Ellis, 1995;Walters, 1995;Barker et al, 2002, and references therein). Recent investigations also consider the fact that the sweet-taste perception is mediated by a cascade of various biochemical complexes and several structure-taste studies have been performed on cyclamates and other artificial sweeteners (exemplified by Pautet et al, 1982;Spillane et al, 1989;Suami et al, 1998;Max et al, 2001;Montmayeur et al, 2001;Bassoli et al, 2002;Li et al, 2002;Spillane & Hanniffy, 2003;Morini et al, 2005;Jiang et al, 2005;Nakajima et al, 2006). Some research was also devoted to their solution chemistry Birch, 2002;Birch et al, 2004;Klofutar et al, 1999;Klofutar et al, 2006a,b;Rudan-Tasič et al, 2006).…”

Sulfamic Acid and Its N- and O-Substituted Derivatives

“…Fourteen simple sulfamate esters RNHSO 2 OR′ (R = i Bu, cyc -C 6 H 11 , 2-Me- cyc -C 6 H 11 ; R′ = Me, Et, n Pr, i Pr, i Bu, s Bu, cyc -C 6 H 11 ) were synthesized in a study of the taste of sulfamate esters. Many of these esters were found to be sweet, and thus, this work established that a negative charge on the sulfamate is not necessary for sweetness …”

“…Many of these esters were found to be sweet, and thus, this work established that a negative charge on the sulfamate is not necessary for sweetness. 453 3.3. Reactions 3.3.1.…”