Three compounds were isolated from
Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3
β-ol (lupeol,
1) and 3
β-lup-20(29)-en-3-yl acetate (
2) and the carbohydrate 1,2,3,4,5,6-hexa-
O-acetyldulcitol (
3);
lupeol was also isolated from
Xylosma flexuosa.
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Three compounds were isolated from
Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3
β-ol (lupeol,
1) and 3
β-lup-20(29)-en-3-yl acetate (
2) and the carbohydrate 1,2,3,4,5,6-hexa-
O-acetyldulcitol (
3);
lupeol was also isolated from
Xylosma flexuosa. The compounds’ structures were elucidated by spectroscopic and spectrometric analysis. Compound
1 acts as an energy transfer inhibitor, interacting with isolated CF
1 bound to thylakoid membrane, and dulcitol hexaacetate
3 behaves as a Hill reaction inhibitor and as an uncoupler, as determined by polarography. Chlorophyll
a (Chl
a) fluorescence induction kinetics from the minimum yield F
0 to the maximum yield F
M provides information of the filling up from electrons coming from water to plastoquinone pool with reducing equivalents. In this paper we have examined the effects of compounds
1 and
3 on spinach leaf discs. Compound
1 induces the appearance of a K-band, which indicates that it inhibits the water splitting enzyme.
In vivo assays measuring the fluorescence of chl
a in
P. ixocarpa leaves sprayed with compound
1, showed the appearance of the K-band and the PSII reaction centers was transformed to “heat sinks” or silent reaction centers unable to reduce Q
A. However,
3 also induced the appearance of a K band and a new band I appears in
P. ixocarpa plants, therefore it inhibits at the water splitting enzyme complex and at the PQH
2 site on b
6f complex. Compounds
1 and
3 did not affect chlorophyll
a fluorescence of
L. perenne plants.
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