Struktur der Sesquiterpene von Petasites hybridus (L.) G. M. et SCH.: Neopetasol‐Abkömmlinge

Abstract

Structure of the Sesquiterpenes of Petasites hybridus (L.) C.M. et SCH.: Derivatives of Neopetasoi SummaryThe structure of 5 compounds of the sesquiterpene fraction of petasites hybridus has been determined by combination of spectroscopic methods, especially by analysis of the 360-MHz-'H-NMR. spectra. Most natural products are esters of a sesquiterpene alcohol, which is the 7 8-epimer of petasol. The alcohol is named neopetasol.

New Eremophilane Sesquiterpenes from a Rhizome Extract of Petasites hybridus

“…The 13 C-NMR data of the sesquiterpene skeletons were in perfect agreement with the published data of 2-(angeloyloxy)-8a-H-eremophilanolide (= (8R)-2-[(angeloyl)oxy]eremophil-7(11)-en-12,8-olide; 1) [10]. As Naya et al [11] and Siegenthaler [10] stated, the 8a-epimers of eremophilane lactones can be clearly distinguished from the 8b-epimers by the chemical shifts of the Me (14) and Me (15) groups 1 ). In skeletons with an H a ÀC(8), a non steroid-like conformation is stabilized (Figure), and the H-atoms of the Me(15) group resonate at higher field than those of Me (14).…”

“…In skeletons with an H a ÀC(8), a non steroid-like conformation is stabilized (Figure), and the H-atoms of the Me(15) group resonate at higher field than those of Me (14). In contrast, a steroid-like conformation is stabilized in skeletons with a H b ÀC (8), and, consequently, Me (14) resonates at higher field. Thus, the observed 1 H-NMR chemical shifts of Me(15) (d(H) 0.87) and Me(14) (d(H) 1.13) clearly pointed to 8a-H-eremophilanolides in the case of 1 and 2, more precisely, to cis-decalin structures with Me groups at positions 4 and 5, as well as a C 3 chain at position 7.…”

“…As Naya et al [11] and Siegenthaler [10] stated, the 8a-epimers of eremophilane lactones can be clearly distinguished from the 8b-epimers by the chemical shifts of the Me (14) and Me (15) groups 1 ). In skeletons with an H a ÀC(8), a non steroid-like conformation is stabilized (Figure), and the H-atoms of the Me(15) group resonate at higher field than those of Me (14). In contrast, a steroid-like conformation is stabilized in skeletons with a H b ÀC (8), and, consequently, Me (14) resonates at higher field.…”

“…By NMR, the structure of 4 was determined as (8R)-2-[(methacroyl)oxy]eremophil-7(11)-en-12,8-olide. This is the first isolation of an eremophilanolide with a methacroyl (= 2-methylprop-2-enoyl; Met) side chain, although neopetasol derivatives esterified with methacrylic acid were previously isolated from the rhizome extracts of P. hybridus [14].…”

“…The Table 2) and in 3 ( Table 1). In contrast to the structure elucidation described for 2, the Me(15) group was shifted to lower field than that for Me (14). Therefore, the conformation of 8 was steroid-like, and the compound was identified as (8S) (15) and Me (14) with those of other 8b congeners, the orientation of the 8-OH group was assumed as b.…”