The heterocyele in (4) is a masked fused ring held in abeyance.
中的杂环可以看作是一个被掩蔽的，处于暂时停顿状态的稠环。
In fused-ring and bridged-ring compounds two carbons are common to the two rings.
在稠环和桥环化合物中，两个碳原子是两个环公用的。
Nitrogenous fused-ring derivatives, medicinal compositions containing the derivatives, and use thereof as drugs.
含氮稠环衍生物，含该衍生物的药物组合物，和其作为药物的用途。
Bicyclic fused aziridines can generate regioselective ring opening reaction with various alcohols, catalyzed by slight concentrated sulfuric acid.
用醇作溶剂、微量的浓硫酸作催化剂，稠合双环氮杂环丙烷衍生物可发生区域选择性氮杂环开环反应。
Conclusion The modification of a 1,4-oxazine-2-one ring fused with positions 9 and 10 of A-ring will reduce the antitumor activity of camptothecins.
结论喜树碱A环的9，10位增加一个“1，4 氧嗪2 酮”六元环后，其抗肿瘤活性要比喜树碱或10 羟基喜树碱的活性降低。
Conclusion The modification of a 1,4-oxazine-2-one ring fused with positions 9 and 10 of A-ring will reduce the antitumor activity of camptothecins.
结论喜树碱A环的9，10位增加一个“1，4 氧嗪2 酮”六元环后，其抗肿瘤活性要比喜树碱或10 羟基喜树碱的活性降低。
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