Agents of formula: where R1 and R2 vary independently and are acyl, sulfonyl, phosphoryl, alkyl, substituted alkyl, halogen, aryl, arylalkyl, substituted aryl, heteroaryl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, heterocycle, or heteroatoms and R3 is H or a member of a ring structure which includes R2, are provided as are agents of formula: where R1, R2 and R3 vary independently and: R1=OH, OR′, NHR′, NR′R″ (with R′ R″=alkyl, aryl, heteroaryl, etc) R2=acyl, alkyl, aryl, sulfonyl, etc R3=alkyl, aryl, substituted aryl, heteroaryl, etc and R4 and R5 are (independently) H, methyl or alkyl, substituted alkyl, aryl, substituted aryl, etc. Methods of using the agents to treat e.g. cardiovascular disease, stroke, shock, injuries caused by hypoxia, male erectile dysfunction, and Alzheimers are provided.
