Selection of amino alcohols. To probe the structural requirements of amino alcohols that can ring-open G>P, we investigated the importance of the proximity of the hydroxyl group (pro-nucleophile) and the amino group (general base). Accordingly, we prepared solutions of G>P and propanolamine (PrA), butanolamine (BuA), or pentanolamine (PeA) at pH 9.5. Upon heating at 40°C for one week, the cumulative yields of glycerophosphodiesters (GPXs) derived from PrA and BuA were 4 and 8 times lower, respectively, than those obtained with EA (Fig. and S23-S25). No phosphodiesters resulted from ringopening of G>P by PeA ( 31 P-NMR). These results suggest that amino alcohols catalyze their own addition to G>P (i.e., their amine acts as an internal general base). Thus, as the amino and hydroxyl groups are placed further apart, expanding the size of the cyclic transition state for general base catalysis from a five to an eight-membered ring, addition to G>P becomes progressively less favored (Fig. ).