| 摘要 |
A compound of the following formula: <IMAGE> (II) <IMAGE> (VIII) <IMAGE> (IX) wherein: R1 and R2 is hydrogen or C1-4 alkyl or R1 and R2 together are C2-5 polymethylene; R3 is hydroxy, C1-6 alkoxy or C1-7 alkylcarbonyloxy; R'4 is ethyl, isopropyl, t-butyl or cyclopentyl, and R16 is hydrogen or C1-6 alkyl.
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