Neolignans structure

Investigations on the ethanolic extract from the bark of T. yunnanensis led to the isolation of two new neolignans. One of them was named taxuyunin A, and has a neolignan structure containing a sugar xylose, while the other neolignan, taxuyunin B, carries a rare C-3 side chain [87]. 

In an analogous fashion, use of the 7r-bonds of vinyl ethers, vinyl sulfides, and electron-rich styrenes as nucleophiles has been developed as a surprisingly versatile anodic C-C bond-forming reaction, particularly for the synthesis of complex neolignan structures. Early controlled-potential electrolysis studies on pam-methoxyphenol and vinyl ethers gave the corresponding dihydrobenzofuran acetals in what is formally a [3 2]-... 

Compound 34 was isolated as being yellowish amorphous. The FD-MS spectrum of 34 exhibited an M at m/z 582. In the EI-MS spectrum of 34, peaks at m/z 386, 180, 151 and 137 were observed as principal ions. A prominent peak at m/z 386 could be assigned to neolignan structure 30. A large peak at m/z 180 could be due to a coniferyl alcohol ion derived from an arylglycerol moiety in structure 34. The spectrum of the acetate 34a (Table 4.3) showed it to be a mixture of threo and erythro isomers. Two doublets at 5 6.08 (J=5.5 Hz) and 6.15 (J=6.1 Hz) were attributed to H-7" in an arylglycerol structure for erythro and threo isomers, respectively. The relative... 

Table 7.3.5. Neolignan structures classified according to skeletal types and subtypes...

Amongst the plant neolignans one finds some 2-methylenetetrahydrofurans of which burchellin (146) (lignan numbering) is an example. In this series the structures, stereochemistry and absolute configurations have been established by a combination of... 

Many natural products display structural motifs biosynthetically derived from ortho-quinol precursors, and some even feature ortho-quinol moieties in their final structural arrangement [1, 6]. Asatone (7) and related neolignans can be put forward as classic examples of complex natural products derived from cyclodimerization of oxidatively activated simple phenol precursors (Figure 5) biomimetic syntheses of 7 have accordingly been accomplished by anodic oxidation (Section 15.2.1) and by Pelter oxidation (Section 15.2.2) of the naturally occurring phenol 9 [34, 36]. 

Fig. 9C.8 Structures of lignans and neolignans isolated from a German Riesling wine...

From the viewpoint of organic synthesis, nature provides us with a number of target molecules, which have novel structures and a variety of biological activities. As already shown in Section II.A, electrochemical oxidation of phenols has been applied successfully to natural products synthesis. Hypervalent (diacyloxyiodo)benzenes have also been proved to be effective for natural products synthesis. Generally, oxidation of o- and p-methoxyphenols in MeOH provides the corresponding o- and p-quinone monoketals, respectively. They are utilized as promising synthons for natural products and related bioactive compounds, as demonstrated by Swenton . Recently, these quinone monoketals have been utilized for syntheses of terpenoids, neolignans, anthraquinones, alkaloids and related compounds. 

Costa, M.C.A. and Takahata, Y. (2003) Core electron binding energy (CEBE) shifts as descriptors in structure-activity relationship (SAR) analysis of neolignans tested against Loishmania donovcmi. 

Wallis, A. R A. (1998) Structural diversity in lignans and neolignans. In Lewis, N. G., and Sarkanen, S. (eds). Lignin and Lignan Biosynthesis, American Chemical Society, Washington, DC. 

Three neolignans (15, 16 and 17) were isolated from the wood of A. sachalinensis, and their structure was elucidated by spectroscopic analyses, they were identified with 2,3-dihydro-2-(4-hydroxy-3-methoxyphenyl)-3-hydroxymethyl-5-(2-formylvinyl)-7-hydroxybenzofuran (15), 2,3-dihydro-2-(4-hydroxy-3-methoxyphenyl)-3-(p-coumaroyloxymethyl)-5-co-hydroxypropyl-7-hydroxybenzofuran (16) and 1-(4-hydroxy-3-methoxyphenyl)-2-[4-(2-formylvinyl)-2-methoxy-phenoxy]-propane-1,3-diol (17). The absolute configurations of the former two neolignans (15) and (16) have been demonstrated, using CD data and shifts (ref. 20). 

This section deals with the structural elucidation of lignans, neolignans and sesquilignans obtained from the wood of S. sachalinensis (refs. 37,38,39). 

This section reviews the structural elucidation of neolignans and sesquilignans from the bark of Eucommia ulmoides. 

The neolignans possess many different structures and are divided into more than fifteen subgroups. They include benzofuran, dihydrobenzofuran, diarylethane, benzodioxin, alkyl aryl ether and bicyclo[3.2.1]octane derivatives among others... 

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