Synthetic and spectroscopic studies on the structures of uniflorines A and B: structural revision to 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine alkaloids
作者:Andrew S. Davis、Thunwadee Ritthiwigrom、Stephen G. Pyne
DOI:10.1016/j.tet.2008.02.110
日期:2008.5
diastereoselective synthesis of the C-2 epimer and the C-1, C-2 di-epimers of the putative structure of the alkaloid uniflorine A has been achieved. The synthesis of the latter di-epimers employed a novel pyrrolo[1,2-c]oxazin-1-one precursor to allow for the reversal of π-facial diastereoselectivity in an osmium(VIII)-catalyzed syn-dihydroxylation (DH) reaction. The NMR spectral data of these epimeric compounds
已经实现了生物碱单花碱A的推定结构的C-2差向异构体和C-1,C-2二表位异构体的非对映选择性合成。后者二差向异构体的合成中使用的新颖的吡咯并[1,2- c ^ ]恶嗪-1-酮的前体,以允许π面部非对映选择性的逆转在锇(VIII) -催化顺-二羟基化(DH)反应。这些差向异构化合物和相关异构体的NMR光谱数据与天然产物的NMR光谱数据不匹配。通过将单花素A和B与木麻黄素和已知的合成的1,2,6,7-四羟基-3-羟甲基吡咯烷核苷异构体的NMR数据进行比较,我们明确地得出结论,单花素B是已知的生物碱木麻黄。尽管我们无法通过原始材料和数据明确证明单花青素A的结构,但已发表的数据表明,天然产物也是具有相同相对C-的1,2,6,7-四羟基-3-羟甲基吡咯烷核苷7–C-7a–C-1–C-2–C-3立体化学为木麻黄。因此,我们认为单花青素A是6-表位-酪氨酸。