Phenylpropanoid units

Neolignans are also compounds composed of two phenylpropanoid units, but linked in a manner other than C8-C8 (Fig. 12.1) [10]. The compounds of this class are often chiral and naturally occurring neolignans are usually optically active, which evokes the involvement of DPs in the biosynthesis of neolignans. 

All these data support the concept of preferential liberation of the phenylpropanoid units, followed by the secondary degradation involving carbon-carbon bond cleavage to the other identified compounds. 

Lignins are a group of macromolecular heteropolymers (600-1000 kDa) found in the cell wall of vascular plants that are made up of phenylpropanoid units. Lignin has proven to be a useful chemical biomarker for vascular-plant inputs to estuarine/coastal margin sediments. Cellulose, hemicellulose, and lignin generally make up > 75% of the biomass of woody plant materials. 

Lignins a group of macromolecular heteropolymers (600-1000 kDa) found in the cell wall of vascular plants that are made up of phenylpropanoid units. 

Shikimic acid pathway chemical pathway common in plants, bacteria, and fungi, where aromatic amino acids (e.g., tryptophan, phenylalanine, tyrosine) are synthesized, thereby providing the parent compounds for the synthesis of the phenylpropanoid units in lignins. 

In this section metabolites bearing one or more alkyl groups directly attached to the C-18 p-terphenyl core will be reviewed, including the xylerythrin group, which is originated through insertion of a third phenylpropanoid unit (See Section 5). 

Lignin classification based on the quantities of the three phenylpropanoid units, namely 4-hydroxyphenylpropane (H), guaiacylpropane (G), and syringylpropane (S), formed in the pyrolysis of lignocellulosic materials... 

An intriguing problem in the structure elaboration of coumarinolignans is the determination of the exact mode of linkage of the phenylpropanoid unit to the coumarin nucleus or, in other words, to decide which of two possible regioisomers the compound in question may be. This difficulty arises because no significant differences in conventional H- and NMR spectroscopic data are expected between two isomers under consideration and hydrogenolysis of the benzyl ether linkage has so far been unsuccessful. One of the earliest NMR methods used to... 

The number of unsaturated sites of cleomiscosin A was calculated [(C+1) - H/2] as 12, but this partial structure has only 11 unsaturated sites, and therefore an additional ring by participation of the oxide functions was reasonable. Cleomiscosin A was thus considered to be a coumarin linked with a phenylpropanoid unit through a dioxane bridge. As mentioned previously, such compounds are known to undergo RDA cleavage on electron impact in a mass spectrometer (75) to give rise to characteristic fragment ions for an olefin (F) and a substituted catechol (E), as shown in Fig. 8. 

Flavonolignans are not merely products formed by oxidative coupling of a phenyl-propanoid unit with a typical flavone, since this term embraces all such products derived from other flavonoid types, viz. flavonols, chalcones, catechins, and others. However, plant constituents like rhodiolinin (103) (725) and the iryantherins (104) 126-129), in which a phenylpropanoid unit is linked with the A ring of the flavone nucleus, would be more appropriately termed lignoflavonoids (726) rather than... 

The exact flavonoid nucleus and the substituted phenylpropanoid unit present in a flavonolignan molecule can be predicted from these fragment ions. The fragment ion at m/z 302 (H), observed in the silybin derivatives, indicates that these are... 

There are just two reports on the isolation of flavonolignans in which C-6 and C-3 of the flavone unit are linked, respectively, to C-7 and C-8 of a phenylpropanoid unit, to form a cyclohexane bridge. Neohydnocarpin (80), isolated from the seeds of Hydnocarpus wightiana (113), and compound 2 (65), isolated from Avena sativa (118), have such a C-C bond linkage between the flavone nucleus and the phenylpropanoid unit. 

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