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. 2021 Feb 2:17:334-342.
doi: 10.3762/bjoc.17.31. eCollection 2021.

Synthesis of legonmycins A and B, C(7a)-hydroxylated bacterial pyrrolizidines

Wilfred J M Lewis  1 , David M Shaw  2   3 , Jeremy Robertson  1
Affiliations

Synthesis of legonmycins A and B, C(7a)-hydroxylated bacterial pyrrolizidines

Wilfred J M Lewis et al. Beilstein J Org Chem. .

Abstract

A one-flask, two-step procedure from 3-amino-2-methyl-5,6,7,7a-tetrahydro-1H-pyrrolizin-1-one affords the Streptomyces secondary metabolites legonmycins A and B - three operations overall from methyl N-Boc-prolinate. The key step proceeds in each case via N,O-diacylation, then selective oxidative hydrolysis of the intermediate bicyclic pyrrole and establishes a precedent for the synthesis of related C(7a)-hydroxylated pyrrolizidines.

Keywords: acyloxypyrroles; bacterial pyrrolizidines; cyanoketones; legonmycin; vinylogous ureas.

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Figures

Figure 1
Figure 1
The clazamycins, and selected bacterial pyrrolizidines of the vinylogous urea type. For consistency, the standard numbering convention used for the plant pyrrolizidines, as depicted for the clazamycins, is used throughout.
Figure 2
Figure 2
Key species in the biosynthesis of legonmycins A (3) and B (4), and the pyrrolizixenamides A–D (9–12).
Scheme 1
Scheme 1
Preparation of the legonmycin core.
Scheme 2
Scheme 2
Hypothesis for the oxidative hydrolysis of diacylated pyrrolizidinone 18 (R = iBu).
Scheme 3
Scheme 3
Preparation of C(7a)-functionalized pyrrolizinone derivatives and synthesis of legonmycins A and B.
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