Abstract
Curcumin is the major phenolic compound present in turmeric (Curcuma longa L.). Curcumin and 15 novel analogs were investigated for their antioxidant and selected biological activities. Strong relationships between the structure and evaluated activity revealed that the compounds with specific functional groups and carbon skeleton had specific biological profiles. Among the compounds tested, the derivatives (E)-2-(3,4-dimethoxybenzylidene)-5-((E)-3-(3,4-dimethoxyphenyl)acryloyl)cyclopentanone (3e), and (E)-2-(4-hydroxy-3-methoxybenzylidene)-5-((E)-3-(4-hydroxy-3-methoxyphenyl)acryloyl)-cyclopentanone (3d) and the parent compound curcumin exhibited the strongest free radical scavenging and antioxidant capacity. Concerning the other biological activities studied the compound (E)-2-(4-hydroxy-3-methoxybenzylidene)-5-((E)-3-(4-hydroxy-3-methoxy-phenyl)-acryloyl)cyclopentanone (3d) was the most potent angiotensin converting enzyme (ACE) inhibitor, while the derivatives (E)-2-(4-hydroxybenzylidene)-6-((E)-3-(4-hydroxyphenyl)acryloyl)cyclohexanone (2b), (E)-2-(3,4-dimethoxybenzylidene)-6-((E)-3-(3,4-dimethoxyphenyl)acryloyl)cyclohexanone (2e) and (E)-2-(3,4-dimethoxybenzylidene)-5-((E)-3-(3,4-dimethoxyphenyl)acryloyl)cyclopentanone (3e) exhibited strong tyrosinase inhibition. Moreover, (E)-2-(3,4-dimethoxybenzylidene)-6-((E)-3-(3,4-dimethoxyphenyl)-acryloyl)cyclohexanone (2e) was also found to be the strongest human HIV-1 protease inhibitor in vitro among the tested compounds. Cytotoxicity studies using normal human lung cells revealed that the novel curcumin as well as its carbocyclic analogs are not toxic.
Highlights
Curcumin [(1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione or diferuloylmethane, 1, Figure 1] is a naturally occurring phenolic compound derived from Curcuma longa L, commonly called turmeric [1]
The antioxidant activity of curcumin and its fifteen carbocyclic analogs belonging to two series were evaluated by subjecting them to the widely used 2,2-diphenyl-1-picrylhyadrazyl (DPPH·) free radical scavenging, ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) assays
The results showed that curcumin followed by compounds 3c and 3f showed strongest antioxidant capacity (1.09 mM TE/L)
Summary
Curcumin [(1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione or diferuloylmethane, 1, Figure 1] is a naturally occurring phenolic compound derived from Curcuma longa L, commonly called turmeric [1]. Apart from its well-studied antioxidant potential, curcumin has received attention due to its anti-HIV, cardioprotective and other therapeutic properties [8]. Curcumin and its analogs have shown decreased melanin production and tyrosinase inhibition, acting as potential anti-melanoma drugs leads [12,13]. Active anti-retro therapy (HAART) and other drugs have been developed to inhibit enzymes like proteases and reverse transcriptase that facilitate HIV life cycle [15]. The antioxidant activity and biological properties of novel carbocyclic curcumin analogs in relation to structural specifications have not been reported. Our present study aimed at exploring structure-activity relationship for antioxidant, anti-hypertensive, anti-melanoma and anti-HIV properties of curcumin and fifteen novel carbocyclic curcumin derivatives (series 2 and 3, Figure 1)
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