Thirty one new sodium heterosulfamates, RNHSO 3 Na, where the R portion contains mainly thiazole, benzothiazole, thiadiazole and pyridine ring structures, have been synthesized and their taste portfolios have been assessed. A database of 132 heterosulfamates (both open-chain and cyclic) has been formed by combining these new compounds with an existing set of 101 heterosulfamates which were previously synthesized and for which taste data are available.Simple descriptors have been obtained using (i) measurements with Corey-Pauling-Koltun (CPK) space-filling models giving x, y and z dimensions and a volume V CPK , (ii) calculated first order molecular connectivities ( 1 χ v ) and (iii) the calculated Spartan program parameters to obtain HOMO, LUMO energies, the solvation energy E solv and V SPARTAN . The techniques of linear (LDA) and quadratic (QDA) discriminant analysis and Tree analysis have then been employed to develop structure-taste relationships (SARs) that classify the sweet (S) and non-sweet (N) compounds into separate categories. In the LDA analysis 70 % of the compounds were correctly classified (this compares with 65 % when the smaller data set of 101 compounds was used) and in the QDA analysis 68 % were correctly classified (compared to 80 % previously). TheTree analysis correctly classified 81 % (compared to 86 % previously). An alternative Tree analysis derived using the Cerius2 program and a set of physicochemical descriptors correctly classified only 54 % of the compounds.
A data set of 101 hetero-(both cyclic and open chain) sulfamate sodium salts, whose taste data are known, have been assembled and divided into sweet (S) (20 compounds) and non-sweet (N) (81 compounds) categories. The data set is made up of 56 compounds reported earlier, 32 synthesised in this work and another 13 reported since the earlier publications. Using the parameters x, y and z (measured for the RNH portion of RNHSO 3 Na using CPK models) and first order molecular connectivity, 1 χ ν it has been possible to achieve a correct classification rate of approximately 65% using linear discriminant analysis (LDA): a compound is N if Ϫ3.285 ϩ 0.439x ϩ 0.662y ϩ 0.236z Ϫ 1.27 1 χ ν > 0 otherwise it would be S. Using quadratic discriminant analysis (QDA) the classification rate increased to approximately 80%. Finally a Tree-based analysis gave an 86% classification rate but performed poorly in classifying correctly the S group of compounds.
Forty-two new disubstituted phenylsulfamates have been synthesized, and 30 of these have been combined with 40 already available from earlier work to create a training database of 70 compounds. On the basis of panel taste data these were divided into three categories, N (nonsweet), N/S (nonsweet/sweet), and (S) sweet, and a "sweetness value" or weighting was also calculated for each compound. Using these 70 compounds as a training set and a series of nine predictors derived from Corey-Pauling-Koltun (CPK) models, calculated from the PC SPARTAN PRO program and Hammett sigma values taken from the literature, a classification and regression tree analysis (CART) was carried out leading to a regression tree that correctly classified 62 of the 70 compounds (89% overall correct classification). The tree's predictive ability varies for the different taste categories, and for nonsweet compounds it is virtually 100%; for nonsweet/sweet compounds it is 66%, and for sweet compounds it is approximately 75%. This tree correctly predicted taste categories for 10 compounds from a test set of 12 randomly selected from among the 42 new compounds (83% correct classification). Therefore, it can be used with a good degree of confidence to predict the tastes of disubstituted phenylsulfamates. For the design of new sweeteners, appropriate values or ranges of the descriptors are derived.
A total of 28 new five-membered aromatic ring thiazolyl-, benzothiazolyl-, and thiadiazolylsulfamates, as their sodium salts, have been synthesized and combined with 30 known similar heterocyclic sulfamates to create a database for the study of structure-activity (taste) relationships (SARs) in this heterocyclic subgroup, which is known to contain a somewhat disproportionate number of sweet compounds compared to other groups of tastants. A series of nine parameters (descriptors) to describe the properties of the sulfamate anions were calculated in Spartan Pro and HyperChem programs. These are the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), length of the molecule, dipole moment, area, volume, E(solv), sigma (from the literature), and log P. The taste data for all 58 compounds were categorized into three classes, namely, sweet (S), nonsweet (N), and nonsweet/sweet (N/S). Discriminant analysis only classified 44 of the 58 compounds correctly. Classification and regression tree analysis (CART) using the S_ Plus program proved highly effective, in that the derived tree correctly classified 46 compounds from a training set of 48 and, from a computer randomly selected test set of 10 compounds, 7 had their taste correctly predicted. A second tree was grown using the additional taste category N/S, and this tree also performed extremely well, with 8 of the 10 compounds in the test set correctly classified. These trees should be very reliable for predicting the tastes of other heterocyclic sulfamates, which belong to the subset used here.
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