| 摘要 |
This invention provides compounds of the structure <IMAGE> where R1 is C3-C20 alkyl or arylalkyl; R2 is hydrogen, loweralkanoyl, loweralkylsulfonyl, loweralkoxycarbonyl, carbamoyl or <IMAGE> wherein X is an alkylene group having from 2 to 4 carbon atoms; and R3 and R4 are the same or different members of the group consisting of hydrogen or loweralkyl, or R3 and R4 taken together form a 5-, 6-, or 7-member heterocyclic ring; and the pharmaceutically acceptable acid addition salts thereof.
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