A New Synthesis of Model Compounds for the beta-5 Structural Unit in Lignins.

Brunow, Gösta; Lundquist, Knut; Carlström, Kjell; Sköldefors, Holger; Wilking, Nils; Theve, Nils Olof

doi:10.3891/acta.chem.scand.38b-0335

Cited by 17 publications

(13 citation statements)

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“…48 In our case, the lipase from Pseudomonas cepacia acylated the dextrorotatory enantiomer of 36 possessing 2S;3R absolute configuration much faster than its levorotatory antipode with 2R;3S absolute configuration. Therefore, the latter enantiomer [(−)-36] could be obtained in optically active form (ee > 90%) by a simple twofold resolution process, as depicted in Scheme 5.…”

Section: H-nmr Data With That Of the Racemic Cis-2-phenyl-3-methoxycamentioning

confidence: 96%

Chiroptical properties of 2,3‐dihydrobenzo[b]furan and chromane chromophores in naturally occurring O‐heterocycles

et al. 2001

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The correlation between the helicity (absolute conformation) of the O-heterocyclic ring of chiral 2,3-dihydrobenzo[b]furan (1) and chromane (2) derivatives and their (1)L(b) band CD was investigated. The same helicity rule was found for both unsubstituted chromophores: P/M helicity of the heterocyclic ring leads to a negative/positive CD within the (1)L(b) band. While the substitution of the fused benzene ring by achiral substituents does not change this helicity rule for the chromane chromophore, it leads to its inversion for the 2,3-dihydrobenzo[b]furan chromophores. On the basis of these observations, the published absolute configurations of natural flavonol and pterocarpan derivatives were confirmed and the configurational assignments of several natural neolignans revised.

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Section: H-nmr Data With That Of the Racemic Cis-2-phenyl-3-methoxycamentioning

confidence: 96%

Chiroptical properties of 2,3‐dihydrobenzo[b]furan and chromane chromophores in naturally occurring O‐heterocycles

et al. 2001

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“…The synthesis of the phenylboronates 5-7 of ß-5 lignin models 2-4 has shown that the stereochemistry is indeed erythro s previously reported (Brunow and Lundquist 1984). The evidence for the configuration (coupling constants in a 6-membered ring) is more conclusive than that obtained from non-rigid propane-l,3-diacetates.…”

Section: Discussionmentioning

confidence: 68%

“…Synthesis of ß-5 Model Compounds*Ĉ ompound 2 was synthesised by the method of Brunow and Lundquist (1984) and compounds 3 and 4 (see Fig. 3 and footnote) by a modification of this route (Ralph et al 1986).…”

Section: Resultsmentioning

confidence: 99%

“…Compound 2 was synthesised following the method of Brunow and Lundquist (Brunow and Lundquist 1984), in 30% overall yteld.…”

Section: Synthetic Methodsmentioning

confidence: 99%

“…In a recently published paper (Chen et al 1985), ß-1 model compound isomers were misassigned, since the assignments were based on the ß-ether erythro/threo nomenclature. The unambiguous R/S nomenclature is given in Figs The stereochemistry of the propyl sidechains in the ß-5 model l, synthesised by Brunow and Lundquist, had previously been assigned äs erythro (Brunow and Lundquist 1984) based on comparisons of the *H NMR coupling constants of the tetra-acetate with a ränge of previously synthesised compounds (Kristersson and Lundquist 1980;Ahvonen et al 1983). These assignments were, in turn, based on comparisons of 1 H NMR coupling constants with related compounds (Nakatsubo and Higuchi 1975;Ferrand and Huet 1975) whose stereochemistries were determined from NMR spectra of the corresponding phenylboronates or acetals.…”

Section: Introductionmentioning

confidence: 99%

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The Stereochemistry of β—5 Lignin Model Compounds

Ede¹,

Ralph²,

Wilkins³

1987

Holzforschung

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Keywords ß-5 Lignin model compound Phenylcoumaran Phenylboronate Stereochemistry NMR X-ray crystallography DihydrodehydrodiisoeugenolThe Stereochemistry c/ß-5 Lignin Model Compounds Summary A ränge of chemical and spectroscopic techniques were used to determine the Stereochemistry of several ß-5 lignin model compounds. In phenylboronate derivatives of the model compounds, the torsional angles implied by the NMR coupling constants in the six-membered ring (J a p = 4 Hz, Jß Y " = 10-12 Hz) confirmed their erythro Stereochemistry. The conformation of the phenylboronatesgave rise to shielding, and consequent unusual spectral dispersion of the aromatic lignin dimer protons in thetr NMR spectra. This allowed the complete assignment of the and I3 C NMR spectra by use of the 2D I3 O'H shift correlation pulse sequence. A threo acetal of one model was synthesised, but synthesis of the threo model itself was not achieved. The NMR spectrum of the threo acetal, with J ep = 10 Hz, indicated an axialaxial arrangement of Ha and Hß, which confirmed the threo configuration. Also reported is an X-ray diffraction crystal structure of dihydrodehydrodiisoeugenol which confirms the chemically predicted erythro Stereochemistry.

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