Novel compounds of formula (I) are described wherein: R1=(CH2)mCH3
where m is 0 or an integer in the range from 1 to 16, or an alkenyl, alkynyl, alkoxy,
alkylthio, or alkyl sulfinyl group having from 2 to 17 carbon atoms; R2=H,
CH3 or CH2CH3; R3=H or CH3;
R4H or CH3; R5=lower alkyl having from 1 to 5
carbon atoms; n is an integer in the range from 1 to 3, and X is carboxyl (COOH)
or carbalkoxy (COOR5), cyano (CN), phosphonic acid (PO3H2),
phosphonate ester (PO3[R5]2) or 5-tetrazole, and
pharmaceutically acceptable salts thereof. Preferably, the compounds are optically
pure enantiomers of the R— or S—configuration in which R3=R4=R5=H,
R2=CH3 and R1 is a saturated aliphatic chain of
one to five carbon atoms. The compounds are useful as cellular rescue agents
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