LR16, a compound with potent effects on the oxygen affinity of hemoglobin, on blood cholesterol, and on low density lipoprotein.

2-[4-(3,4-Dichlorophenylureido)phenoxy]-2-methylpropionic acid, LR16, combines with two symmetrically related sites in the central cavity of deoxyhemoglobin, 20 A away from the binding site of 2,3-bisphosphoglycerate, and acts as an allosteric effector synergistic with 2,3-bisphosphoglycerate. LR16 (1 mM) raises P50, the partial pressure of oxygen needed to achieve half-saturation with oxygen of a hemolysate of human hemoglobin, about 50 times more strongly than 1 mM 2,3-bisphosphoglycerate. Oral administration of LR16 (at small doses that produced no ill effects) to rats that were fed a diet rich in cholesterol caused substantial reductions of total serum cholesterol and low density lipoprotein-cholesterol, while high density lipoprotein-cholesterol remained unchanged.