Lienhard Hoesch

Protocatechualdehyde and other phenols as cell wall components of grapevine leaves

Abstract Upon washing with dilute bicarbonate solution, quercetin glucuronide as well as the monotartaryl esters of 4-coumaric, caffeic and ferulic acids were released from extensively solvent-purified cell wall material (CWM) of Vitis vinifera leaves. Drastic alkaline hydrolysis additionally yielded protocatechualdehyde and protocatechuic acid. Digestion of bicarbonate-washed CWM with a commercial esterase liberated protocatechuic and 4-coumaric acids, but no protocatechualdehyde. The latter was, however, solubilized upon incubation of the same CWM with pectinase (‘Macerase’) and subsequent alkaline hydrolysis, together with some of the two phenolic acids. In contrast to this, the analogous set-up with cellulase was almost ineffectual, inasmuch as only traces of these acids were released. Thus, quercetin glucuronide and the tartaric esters of the hydroxycinnamic acids are only loosely associated with the cell wall, whereas part of the 4-coumaric and protocatechuic acids as well as the protocatechualdehyde are covalently ester-bonded. The phenolic acids probably act as the acyl parts of esters with polysaccharidic hydroxyl groups, and the aldehyde as the hydroxyl part of esters with glucuronic or galacturonic acid moieties. The contents of extractable protocatechualdehyde and protocatechuic acid decreased by about 60% from the early to the late exponential phase of leaf growth. The possibility is discussed that the decrease in covalently wall-bound protocatechuic compounds during leaf development is causally related to the age-dependent establishment of resistance to fungal disease.

The constitution of vertinolide, a new derivative of tetronic acid, produced by Verticillium intertextum☆

Abstract From the culture of Verticillium intertextrum a new tetronic acid derivative, vertinolide, has been isolated as the main constituent of the chloroform extract. Structure 1a was established for vertinolide by X-ray diffraction analysis. Vertinolide (1a) was also transformed to an O-methyl-(1b), an O-acetyl-(1c), a tetrahydro- (1d) and a tetrahydro-O-methyl-derivative (4). The spectroscopic properties of 1a, of its derivatives 1a, 1c, 1d and 4 as well as of three model compounds are compared and discussed.

Inhibition of β-N-Acetylglucosaminidase by Glycon-Related Analogues of the Substrate

Inhibition studies on beta-N-acetylglucosaminidase (EC 3.2.1.30) of widely differing origins (animal, plant, fungus) were carried out with N-acetylglucosaminono-1,5-lactone (1), N-acetylglucosaminono-1,5-lactam (2), 1,5-imino-N-acetylglucosaminitol (3), and N-acetylglucosaminono-1,5-lactone oxime (4). The inhibition was competitive in all cases, and Ki values were generally in the range of 0.15-2 microM, except for the fungal enzyme (5-20 microM). To assess the kinetics of enzyme-inhibitor complex formation, continuous enzyme activity monitoring was done with 3,4-dinitrophenyl-beta-N-acetylglucosaminide as the substrate. A slow approach to the binding-equilibrium in the time scale of minutes could not be observed with any of the inhibitors tested (1-4). The results are evaluated as to the bearing of the enzyme source on best performance of the test compounds, the sub-type of inhibition mechanism is discussed, and suggestions are made for further analogue syntheses as well as potential applications of 1-4 (particularly the O-phenylcarbamoyl derivative of the latter) in biological and medical research.