Conformation Analysis of Aspartame‐Based Sweeteners by NMR Spectroscopy, Molecular Dynamics Simulations, and X‐ray Diffraction Studies

Abstract

We report here the synthesis and the conformation analysis by 1H NMR spectroscopy and computer simulations of six potent sweet molecules, N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-S-tert-butyl-L-cysteine 1-methylester (1; 70 000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-beta-cyclohexyl-L-alanine 1-methylester (2; 50 000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-4-cyan-L-phenylalanine 1-methylester (3; 2 000 times more potent than sucrose), N-[3,3-dimethylbutyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (4; 5500 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (5; 15 000 times more potent than sucrose), and N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (6; 15 000 times more potent than sucrose). The "L-shaped" structure, which we believe to be responsible for sweet taste, is accessible to all six molecules in solution. This structure is characterized by a zwitterionic ring formed by the AH- and B-containing moieties located along the +y axis and by the hydrophobic group X pointing into the +x axis. Extended conformations with the AH- and B-containing moieties along the +y axis and the hydrophobic group X pointing into the -y axis were observed for all six sweeteners. For compound 5, the crystal-state conformation was also determined by an X-ray diffraction study. The result indicates that compound 5 adopts an L-shaped structure even in the crystalline state. The extraordinary potency of the N-arylalkylated or N-alkylated compounds 1-6, as compared with that of the unsubstituted aspartame-based sweet taste ligands, can be explained by the effect of a second hydrophobic binding domain in addition to interactions arising from the L-shaped structure. In our examination of the unexplored D zone of the Tinti-Nofre model, we discovered a sweet-potency-enhancing effect of arylalkyl substitution on dipeptide ligands, which reveals the importance of hydrophobic (aromatic)-hydrophobic (aromatic) interactions in maintaining high potency.

Molecular modelling and models in the study of sweet and umami taste receptors. A review.

“…Moreover, the derived sites were used as an entry point for structure‐based modelling by pseudo‐receptor techniques, in this case used only as a tool to evaluate the reliability of the ligand binding sites identified, without essentially altering the architecture of the sites yielded by homology modelling. Confirmation of the predictive power of the obtained models was the good prediction of the sweetness of sweet synthetic compounds which appeared in the literature after the publication of the models (Figure ).…”

Identification and characterisation of the E951 artificial food sweetener by vibrational spectroscopy and theoretical modelling

“…These intermolecular hydrogen bonds contribute to the crystal packing of the E951 molecule and give rise to rows of hydrogen-bonded molecules along two different directions. [11,27] The reason for the hydrogen bond lengths' variation could be attributed to the spatial constriction between the molecules in the crystal, leading to the formation of the hydrogen bonds.…”

“…[26,27] The N-C-R torsional angles of the E951 molecule with values situated between 106.7 • and 124.4 • (Table S1, Supporting Information) may explain the differentiation between its conformation in the solid state and in solution. The intramolecular cyclisation of the E951 molecule in solution is possible for the low-energy conformers and at high temperatures, which suggest that E951 molecule is very flexible.…”

“…3d). [27,47,56,66] In the Raman spectra in the acidic pH range 2-0 (Fig. S3, Table S3 in Supporting Information), new bands appear in the low wavenumber region (700-200 cm −1 ) and are attributed to the carboxylate bending mode (pH 1, 650 cm −1 ), [32] phenylalanine and Amide IV vibrations (pH 1, 624 cm −1 ), [42] Amide VI and C1OO − wagging mode (pH 1, 601 cm −1 ), [32,42] N-C O bending mode and primary saturated aliphatic amides (pH 1, 581 cm −1 ), [67] COO − bending mode (pH 1, 524, 333 cm −1 ), [32,67] ring out-ofplane bending mode (pH 1, 478 cm −1 ).…”

Development of an analytical methodology using Fourier transform mass spectrometry to discover new structural analogs of wine natural sweeteners

“…In general, chemical synthesis is involved in generating these analogs by making slight modifications to the stereochemistry or substituents of the sweetener [22][23][24][25]. However, natural biosynthetic pathways may also cause changes of the same type and several isomers and derivatives of a natural compound are often observed in the same plant [26].…”