A compound of structure (I) wherein R and R1 are each, independently, (A), (B), or hydrogen; R?2 and R3¿ are each, independently, alkyl, arylalkyl, or R?2 and R3¿ may be taken together to form a cycloalkyl ring; R4 is a heterocyclic radical which may be optionally substituted; R5 is alkyl or arylalkyl; R?6 and R7¿ are taken together to form a saturated heterocyclic ring which may be optionally substituted; k=0-1; m=0-1; n=1-6; with the proviso that R and R1 are not both hydrogen, or a pharmaceutically acceptable salt thereof, which is useful as an immunosuppresive, antiinflammatory, antifungal, antiproliferative, and antitumor agent.