Guaiacylglycerol- 3-coniferyl ether

Incubation of coniferyl alcohol with a crude enzyme preparation from Eucommia ulmoides in the presence of hydrogen peroxide resulted in optically active C8-0-C4 neolignan dimers, (+)-eryf/rro-guaiacylglycerol-( >-coniferyl ether (38% e.e.), and (-)-t/ire<9-guaiacylglycerol- 3-coniferyl ether (34% e.e.) (Fig. 12.11) [68]. In... 

In conjunction with a study on the reactivity of dimeric quinone me-thides, Elder et al. (56) examined the physical and electronic structure of guaiacylglycerol-/ -coniferyl ether, which is substituted in a manner representative of the lignin polymer. Calculations were performed using AMBER (Assisted Model Building with Energy Refinement) (24), which is a force-field method, and the energetic minimum was determined to be a folded structure similar to that reported by Gravitis and Erins (55). 

The reaction mechanism for the water addition that converts the QM (3-O-QM into a guaiacylglycerol-(3-coniferyl ether dilignol (GGE) have also been investigated (Scheme 2.22).18... 

Combination of an Ri, radical with an Ra radical yields the single p-qninone methide dimer (V). Here the quinone methide cannot become stabilized by an intramolecnlar addition reaction. Instead, nucleophilic attack of its y-carbon atom occurs by a hydroxyl ion from the medium, for example aromatization and protonation of the phenoxido ion thus formed give rise to guaiacylglycerol- 3-coniferyl ether (VI), again in racemic form dc-spite its two asymmetric carbon atoms. Since attack by the extraneous hydroxyl ion can occur on either side of C-y of the p-quinone methide (V), complete equilibration of the specific hydrogens from the original conifcryl alcohol moiety in the lower half of (V) presumably occurs (sec formulae on p. 131). 

Fig, 6. Mechanism of the formation of guaiacylglycerol-3-coniferyl ether and a guaiacyclglycerol-p.y-diaryl ether [guaiacylglycerol-p,Y-diconi-feryl ether]... 

Guaiacylglycerol-/3-coniferyl ether is a dimeric decomposition product of coniferous lignin dehydrodivanillin may be also formed by dimerization of vanillin after formation from lignin. Among the lignin decomposition products are mono-, di- and triphenol derivatives which are derived from the different types of lignin of needle trees, deciduous trees, or graminees. 

The yield of guaiacylglycerol 0-coniferyl ether (XXII) 31) probably surpasses even pinoresinol (XIX) and dehydrodiconiferyl alcohol (XVII). So far it has not been obtained in crystalline form, possibly because of its labile benzyl alcohol group. A derivative has been obtained in the crystalline state and has also been synthesized 15). Guaiacylglycerol 0-coniferyl ether also occurs to a small extent in spruce cambium and has been isolated from spruce lignin as a crystalline derivative 42). 

Recently, small amounts of guaiacylglycerol 0-coniferyl ether have been isolated by Nimz (35) after percolating pre-extracted sprucewood for 8 days with 2% aqueous acetic acid at 100°C. This particular 0-aryl... 

Guaiacylglycerol 0,7-bisconiferyl ether (XLII) (16) is a labile trilignol formed by addition of coniferyl alcohol onto the dimeric quinonemethide (XXI). It readily loses a molecule of coniferyl alcohol by hydrolysis but is stabilized somewhat as soon as its phenolic group is etherified by further dehydrogenation and interaction with other radicals. 

Guaiacylglycerol /3-coniferyl-7-dehydrodiconiferyl ether (XLIII) 16) is a tetralignol of the same kind as the last trilignol and originates by addition of preformed dehydrodiconiferyl alcohol (XVII) onto the dimeric quinonemethide (XXI). It is more stable as the trilignol (XLII). 

Fig. 4-7. Endwise polymerization (Adler, 1977). A guaiacylglycerol-/3-aryl ether structure (1) is dehydrogenated and after resonance, radical c is coupled with a coniferyl alcohol radical b (cf. Fig. 4-4). The /3-5 coupling product (3) is tautomerized and undergoes intramolecular ring closure (a phenylcoumaran structure, 5).

Kratzl K, Kisser W, Gratzl J, Silbernagel H (1959) 2 Guaiacyl ether of guaiacylglycerol and its conversion to coniferyl aldehyde and other arylpropane derivatives Monatsh Chem 90 771-782... 

The main products of coniferyl alcohol dimerization by peroxidase (Scheme XI) are the neolignans, pinoresinol (XXVII), dehydrodiconiferyl alcohol (XXVni) and guaiacylglycerol-P-O-coniferyl alcohol ether... 

F Berthold, E-L Lindfors, G Gellerstedt. Degradation of Guaiacylglycerol- 3-guaiacyl Ether in the Presence of NaFIS or Poly sulfide at Various Alkalinities. Part II. Liberation of Coniferyl Alcohol and Sulphur. Holzforschung 52 481-489, 1998. 

In conclusion, the structure of con xDund 25 was guaiacylglycerol-p-coniferyl alcohol ether diferulate. 

At the onset of our studies, the only processes known engendering phenolic coupling were catalyzed by H2O2-dependent peroxidase(s), 02-requiring laccases, or phenol oxidases. But such products were racemic, e.g., the coupling of coniferyl alcohol 13 afforded ( )-pinoresinols 20a/20b, ( )-dehydrodiconiferyl alcohols 22a/22b, and ( )-guaiacylglycerol-8-0-coniferyl alcohol ethers 21. 

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