Abstract
Pterosin B is a naturally occurring indanone found in bracken fern (Pteridium aquilinum) that displays a variety of interesting pharmacological properties, but for which few stereoselective syntheses exist. Herein we describe a 7-step stereoselective synthesis of (2R)-pterosin B via 6-bromo-5,7-dimethylindan-1-one whose structure was confirmed by NOE analysis and structure determination by X-ray crystallography. The hydroxyethyl chain was introduced via a Suzuki-Miyaura cross-coupling reaction. The 2-methyl group was introduced stereoselectively by methylation of a SAMP [(S)-1-amino-2-methoxymethyl)pyrrolidine] hydrazone and the chiral auxiliary was removed to produce (2R)-pterosin B. The structure of pterosin B was confirmed by specific rotation and structural determination by X-ray crystallography.
Highlights
Results and discussionPterosins are a group of substituted 1-indanones originally characterized following their isolation from the bracken fern Pteridium aquilinum [1,2,3]
In the synthesis of pterosin B we sought to introduce the hydroxyethyl group directly onto indanone 5 using a SuzukiMiyaura cross-coupling with the benzyl-protected trifluoroborate salt 8 [17]
During our initial attempts to obtain the benzylated indanone 12 (Scheme 3) by ozonolysis, we found that the desired product contained small amounts of a contaminant that was isolated by RP-HPLC
Summary
Results and discussionPterosins are a group of substituted 1-indanones originally characterized following their isolation from the bracken fern Pteridium aquilinum [1,2,3]. Pterosin B (1) occurs naturally as its (2R) isomer and is a decomposition product of the bracken toxin ptaquiloside (2) (Fig. 1). More concise route to (2R)-pterosin B, we envisaged elaboration of the core indanone structure 5 (Fig. 2), described previously by Sheriden and co-workers [12] and describe a stereoselective 7-step synthesis of (2R)-pterosin B and its characterisation by X-ray crystallography.
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