1. A method for improving the oxygen-releasing ability of hemoglobin, hemoglobin variants, recombinant hemoglobin or hemoglobin-based blood substitutes to organs or peripheral tissues in human bodies, by administering a compound of Formula I to a subject in need thereof, wherein the compound of Formula I forms at least one hydrogen bond with ?Arg141 of hemoglobin, strengthening the ?1/?2 interface of hemoglobin, further stabilizing the oxygenated hemoglobin in the low oxygen affinity T state and facilitating the oxygen release to the organs or the peripheral tissues,
wherein R1 is C2-C6 alkyl, C2-C6 alkenyl or C2-C6 alkenol group;
R2 is one or more H or OH; and
R3 and R4 are each independent H or OH or both of them combine together to form a epoxy group.