J. Org. Chem. 1992,57,826-834
826
69.7,58.5,48.5, 37.8; FABMS m / e 929 (M+ + 1); HRMS calcd for C41H78N401&969.4897, found 969.4877. Determination of Binding Constants. For the dimerization study of 29, 15 samples of DMSO-d6 solutions of various concentrations (0.0174.090 M) were prepared and thechemical shifts of the NLH, CLNHz, and C'-NHZ protons of 29 recorded using a Nicolet "-360 NMR (360 MHz) at 23 "C. For the titration of 35 with 37, six separate aliquots (locrZ00 pL) of a 0.53 M was used as the solvent. The crude material was purified by DMSO-d6solution of 37 were added to a 0.086 M solution (600 column chromatography using 5% MeOH/CHC13 as the eluent &) of35 andthechemicalshiftsOftheguanineNLHand G-N'Ht to provide 36 (2.65 g, 75.2%): Rf = 0.48 (system B); 'H NMR protons recorded as a function of relative nucleobaee concen(CDC13) 6 3.38 (3 H, 8, CH30), 3.53-3.72 (64 H, m, CHzO, tration. Data reduction was then effected using standard CH&HZNHCO), 3.86 (2 H, t, J = 6.1 Hz,CHZCHZNHCO), 4.99 Scatchard plots?' Because of the low chemical shift (Ab) vduea (1 H, d, J = 7.3 Hz,O , 7 . 0 3 (1 H, d, J = 7.3 Hz,0 , 7 . 2 3 - 7 . 3 7 involved, the errors are considered to be significantly larger (15 H, m, Trm, 7.51 (1 H, t, CONH); 'gC NMR (CDClJ 6 170.6, 165.3,155.7,146.7,143.6,128.5,128.1,127.4,94.1,71.7,71.0,70.8, (
