| 摘要 |
The present invention provides compounds of formula:
wherein
R a and R b together with the carbon to which they are attached form a group of formula:
where each X 1 is independently selected from hydrogen or substituted or unsubstituted R', OR', -(C=O)R', substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted aralkyl; wherein R' is selected from the group consisting of H, OH, NO 2 NH 2 , SH, CN, halogen, C(=O)H, C(=O)CH 3 , CO 2 H, CO 2 CH 3 , C 1 -C 6 alkyl, alkenyl, alkynyl, aryl, aralkyl and heterocyclic;
where R d is a substituted or unsubstituted R', OR',-(C=O)R', substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, or substituted or unsubstituted aralkyl; wherein R' is selected from the group consisting of OH, NO 2 , NH 2 , SH, CN, halogen, C(=O)H, C(=O)CH 3 , CO 2 H, CO 2 CH 3 , C 1 -C 6 alkyl, alkenyl, alkynyl, aryl, aralkyl and heterocyclic;
R 7 is -OCH 3 and R 8 is -OH or R 7 and R 8 together form a group -O-CH 2 -O-;
R 12a is hydrogen, acyl, alkenyl, or alkyl-O-CO-;
R 21 is -H, OH or CN;
X is -O- or -NH-;
R 5 and R 18 are -OX 1 , wherein each X 1 is independently selected from hydrogen, substituted or unsubstituted C 1 -C 18 alkyl, substituted or unsubstituted C 2 -C 18 alkenyl, substituted or unsubstituted C 2 C 18 alkynyl, substituted or unsubstituted aryl, and -C(=O)R' wherein R' is selected from hydrogen, OH, NO 2 , NH 2 , SH, CN, halogen, C 1 -C 6 alkyl, alkenyl, alkynyl, aryl, aralkyl, and heterocyclic.
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