. . . . . "R2 is ##STR2## wherein R3, R4, R5, R6, R7, R9, and are each independently H, CH3, CH2 NH2, CH2 NHCH3 or CH2 NHC2 H5, and R5, R6, R7, and R9 may also independently be NH2, NHCH3 or NHC2 H5, provided that not more than three of R3, R4, R5, R6, R7, R9, R10 and R25 are other than hydrogen, and if three of these substituents are not hydrogen, at least one of them is methyl; and prodrugs of those compou" . . .