| 摘要 |
A compound of formula I <IMAGE> (I) in which each R1, independently is selected from hydrogen, C1-12alkyl, C1-12alkoxy and halogen; R2 has a significance of R1, independently of R1, or is -OH; R20 is -CO-OR6 or, when each R1 is hydrogen and R2 is 2-C1-4alkoxy, R20 is additionally -OH; R3 is hydrogen or methyl (more preferably hydrogen); and R6 is hydrogen; unsubstituted C6-22alkyl, uninterrupted or interrupted by 1 or 2 oxygen atoms or C1-22alkyl mono- or di-substituted by OH and uninterrupted or interrupted by 1 or 2 oxygen atoms; provided when each RF1 and R2 is hydrogen, then R6 is not hydrogen.
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