Although hemoglobin is probably one of the most extensively studied proteins, the sickling process of deoxy hemoglobin S has yet to be clearly understood. Methods to prevent sickling have been based mainly on chemical modification of the hemoglobin molecule which destabilizes the sickle aggregate sufficiently to prevent fiber formation. Most in vitro chemical modifications of hemoglobin have concentrated on the N-terminal amino groups, or groups close to the N-terminal region. Chemical modification of either N-terminal amino groups of the alpha or beta chains causes different changes in oxygen affinity depending upon which chain is modified. An increase in oxygen affinity of the modified hemoglobin will decrease sickling because of the shift to the oxy-deoxy tetramer equilibrium. In spite of much investigation in this area, a suitable therapeutic agent for sickle cell anemia has not been found. This proposal will investigate the antisickling effects of imidoesters on hemoglobin S in the erythrocyte. The effects of acetamidinated hemoglobin S on sickling, oxygen affinity, red cell survival, and other functional properties of red cells will be examined. The modification sites in both acetamidinated hemoglobin and in crosslinked hemoglobin will be determined. The nature and mechanisms by which crosslinking occurs with monofunctional imidoesters will also be investigated. An attempt to design and synthesize other imidoesters with enhanced specificity towards hemoglobin S without adversely affecting hemoglobin functionality will also be performed.