| 摘要 |
<p>A compound of formula: or a salt thereof wherein: Ra is alkyl, phenyl, C1 to C6 alkylphenyl, or C1 to C6 alkoxyphenyl; Rb is C1 to C6 alkyl; R20 is hydrogen or benzyl; X is C1, I, or benzyloxy; Ry and Rz are taken together to form, methylene (=CH2), or Ry is OR23, and Rz is -CH2OR24, wherein R23 and R24 are each hydrogen or are taken together to form a ting to define a dioxolane, said dioxolane being optionally substituted with -O(C1-4alkyl) or-O(C=O)( C1-4alkyl); and R25 and R26 are both hydrogen, or one of R23 and R26 is hydrogen and the other is acyl; or R25 and R26are taken together to form =CH(OC1-4alkyl) or =CH(OC(=O)C1-4alkyl).</p> |
