- Attrition-enhanced deracemization and absolute asymmetric synthesis of flavanones from prochiral precursors
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Seven racemic 5,7-dimethoxyflavanones afforded conglomerate crystals upon recrystallization from a solvent. Three methodologies were investigated to achieve asymmetric transformation based on dynamic crystallization of the chiral conglomerate system. The first was chiral symmetry breaking of racemic flavanones by attrition-enhanced deracemization. Continuous suspension of racemic flavanones in a small amount of propanol in the presence of a base (1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)) and glass beads promoted chiral symmetry breaking and converted the flavanones to crystals of (+)- or (-)-enantiomers with 78 to 99% ee. The second method involved cyclization of the intermediate aldol product to give optically active flavanone with 90% ee involving a reversible oxa-Michael addition reaction with attrition-enhanced deracemization. The third was a reaction starting from prochiral 2-hydroxy-4,6-dimethoxyacetophenone and 2-naphthaldehyde under basic conditions, which gave the corresponding flavanone in 89% ee.
- Kasashima, Yoshio,Mino, Takashi,Sakamoto, Masami,Shimizu, Waku,Uemura, Naohiro,Yoshida, Yasushi
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p. 5676 - 5681
(2020/10/13)
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- Flavokawains B and C, melanogenesis inhibitors, isolated from the root of Piper methysticum and synthesis of analogs
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The ethanolic extract of the root of Piper methysticum was found to inhibit melanogenesis in MSH-activated B16 melanoma cells. Flavokawains B and C were isolated from this extract based on their anti-melanogenesis activity and found to inhibit melanogenesis with IC50 values of 7.7 μM and 6.9 μM, respectively. Flavokawain analogs were synthesized through a Claisen-Schmidt condensation of their corresponding acetophenones and benzaldehydes and were evaluated in terms of their tyrosinase inhibitory and anti-melanogenesis activities. Compound 1b was the most potent of these with an IC50 value of 2.3 μM in melanogenesis inhibition assays using MSH-activated B16 melanoma cells.
- Jeong, Hye-Jin,Lee, Chang Seok,Choi, Janggyoo,Hong, Yong Deog,Shin, Song Seok,Park, Jun Seong,Lee, John Hwan,Lee, Seokyong,Yoon, Kee Dong,Ko, Jaeyoung
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p. 799 - 802
(2015/02/19)
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- Modulation of human neutrophils' oxidative burst by flavonoids
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Inflammation is a normal response towards tissue injury, but may become deleterious to the organism if uncontrolled. The overproduction of reactive species during the inflammatory process may cause or magnify the damage at inflammatory sites. Flavonoids have been suggested as therapeutic agents to avoid such damage, as these compounds exhibit anti-inflammatory activity, through the modulation of oxidative stress and signalling pathways. Both effects may attenuate neutrophils' activities at inflammatory sites. In this study,we investigated the structure/activity relationship of a series of flavonoids on the oxidative burst of human neutrophils in vitro, as a measure of its anti-inflammatory potential. Neutrophils were stimulated with phorbol-12-myristate-13-acetate, and fluorescence and chemiluminescence techniques were used to evaluate the generation of reactive oxygen species. All the tested flavonoids revealed the ability to modulate the neutrophil 's oxidative burst. From the obtained results, the pivotal role of the catechol group in the B-ringwas evidenced as well as the minor importance of the hydroxylations in the A-ring, which did not appear to be determinant for the activity, although clearly influencing the lipophilicity of the tested flavonoids. It is also clarified the importance of the methylation in the OH group at the B-ring catechol moiety. In conclusion, the obtained results uncover new possible strategies for the resolution of inflammatory processes, using flavonoids to modulate neutrophil's oxidative burst.
- Ribeiro, Daniela,Freitas, Marisa,Tomé, Sara M.,Silva, Artur M. S.,Porto, Gra?a,Fernandes, Eduarda
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p. 280 - 292
(2013/10/01)
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- Investigation of chalcones as selective inhibitors of the breast cancer resistance protein: Critical role of methoxylation in both inhibition potency and cytotoxicity
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ABCG2 plays a major role in anticancer-drug efflux and related tumor multidrug resistance. Potent and selective ABCG2 inhibitors with low cytotoxicity were investigated among a series of 44 chalcones and analogues (1,3-diarylpropenones), by evaluating their inhibitory effect on the transport of mitoxantrone, a known ABCG2 substrate. Six compounds producing complete inhibition with IC50 values below 0.5 μM and high selectivity for ABCG2 were identified. The number and position of methoxy substituents appeared to be critical for both inhibition and cytotoxicity. The best compounds, with potent inhibition and low toxicity, contained an N-methyl-1-indolyl (compound 38) or a 6′-hydroxyl-2′,4′-dimethoxy-1-phenyl (compound 27) moiety (A-ring) and two methoxy groups at positions 2 and 6 of the 3-phenyl moiety (B-ring). Methoxy substitution contributed to inhibition at positions 3 and 5, but had a negative effect at position 4. Finally, methoxy groups at positions 3, 4, and 5 of the B-ring markedly increased cytotoxicity and, therefore, should be avoided.
- Valdameri, Glaucio,Gauthier, Charlotte,Terreux, Rapha?l,Kachadourian, Rémy,Day, Brian J.,Winnischofer, Sheila M. B.,Rocha, Maria E. M.,Frachet, Véronique,Ronot, Xavier,Di Pietro, Attilio,Boumendjel, Ahcène
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scheme or table
p. 3193 - 3200
(2012/06/01)
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