| TUD Organische Chemie | | Immel | | Publications | | Papers | | Abstract 03 | | | View or Print (this frame only) |
Frieder W. Lichtenthaler and Stefan Immel
Sweet Taste Chemoreception (Eds.: M. Mathlouthi, J. A. Kanters, and G. G. Birch), Elsevier Appl. Science, London/New York, 1993, pp. 21-53.
MOLCAD program-mediated calculations of the molecular electrostatic potential (MEP's) profiles and of the respective lipophilicity (hydrophobicity) patterns (MLP's) on the contact surfaces of sucrose, galacto-sucrose, sucralose, and fructose are represented in color-coded form. Most informative with respect to the placement of the tripartite AH-B-X glucophore are the hydrophobicity distributions, which show the lipophilic X-part to be an entire, obviously quite flexible region rather than a specific corner of the "sweetness triangle": in sucrose and sucralose encompassing the outside area of the fructofuranose moiety, in fructose the 1- and 6-CH2 groups in either linked or separated form. In contrast, the hydrophilic portions of these sweeteners are more compact, invariably located opposite to the hydrophobic region, and appear to contain the AH-B couple of the glucophore: the glucosyl-2- and 3-OH group in sucrose and sucralose, versus the 3,4-diol grouping in fructose. Whilst absolute proof for these assignments is still lacking, support for their relevance is derived from the sweetness of altogether 53 sucrose derivatives and some fructose analogs. Most remarkably, the MLP's generated for the solid-state conformations of some non-carbohydrate high-potency sweeteners, such as the sulfamides cyclamate, saccharin, and acesulfame, as well as structurally distinctly different dipeptides, e.g. aspartame, exhibit a hydrophobicity distribution strikingly similar to those observed for the sugars: hydrophilic and hydrophobic areas on opposite sites of the molecule. The results, particularly the lipophilicity patterns presented, sustain the notion, that the sweet receptor with its proteinaceous "hydrophobic cleft" - be it the same for sucrose, fructose, and non-carbohydrate sweeteners or different ones - is quite flexible in adapting to the complementary hydrophobic region of the sweet substance. Following this "docking procedure", the hydrophilic AH-B area of the substrate now being in its proper position, the sweet response is elicited via hydrogen bonding to a complementary receptor-based AH-B couple.
Additional Graphics: Sucrose / High-Potency Sweeteners