ISSN:
0894-3230
Keywords:
Chemistry
;
Theoretical, Physical and Computational Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The acid-base properties of eight 3-aminopropionamidine derivatives R1R2N(CH2)2C((DOUBLE BOND)NH)NR3R4 (1, R1 = R2 = R3 = R4 = H; 2, R1 = R3 = R4 = H, R2 = Me; 3, R1 = R2 = R4 = H, R3 = Me; 4, R1 = R2 = H, R3 = R4 = Me; 5, R1 = Tos, R2 = R3 = R4 = H; 6, R1 = Tos, R2 = Me R3 = R4 = H; 7, R1 = Tos, R2 = R4 = H, R3 = Me; 8, R1 = Tos, R2 = H, R3 = R4 = Me; Tos = 4-toluenesulphonyl) related to the antiviral natural product distamycin A were investigated in water and dimethyl sulphoxide (DMSO). The measured pKa values for the ammonium function in 1-4 in water ranged between 7·48 and 7·73, whereas the corresponding values in DMSO were 9·4 ± 0·3. The amidinium moiety of these compounds displayed pKa values in the range 11·4-12·0 and 13·4-13·6 in water and DMSO, respectively. The tosylamide group in compounds 5-8 was deprotonated in the expected pH region and exhibited pKa values between 9·49 and 10·02 in water, but was considerably less acidic in DMSO (14·5 ≤ pKa ≤ 15·7). The behaviour of the amidinium cation of 5-8 in water and DMSO resembled that of 1-4. The measured pKa values are discussed and the solvent-induced pKa shifts are explained in terms of solvent and substituent effects. The observed pKa differences between the ammonium and the amidinium functions in 1-4 render these compounds suitable intermediates in an alternative synthesis of distamycin A.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
