In order to overcome these difficulties and to improve parameter fitting, prior knowledge can be introduced. A readily available piece of information is the ratio k α /k β = 1.6 ± 0.2 of the mutarotation exchange rates, determined experimentally on a G6P sample at thermal equilibrium from the intensity ratio of the β over α 13 C 1 anomeric signals. In this case, the relaxation rate distributions for both anomeric 13 C 1 , r α and r β , were not significantly different from each other in each experiment, on the basis of our Monte Carlo analysis (see Table ). This conclusion is further supported by experiments reported in ref. where indeed the authors found equal longitudinal relaxation times for C in [U-13 C, U-2 H]-G6P in dDNP experiments. Therefore, because prior knowledge of the ratio k α /k β did not sufficiently constrain all the remaining model parameters, these findings led us to introduce the further hypothesis that both anomers have identical relaxation rates. Results of the parameter fitting for the three experiments obtained with the prior constraints r α = r β and on k α /k β are summarized in Table .