Abstract
A new microwave method (MM) has been developed for the synthesis of a series of 16 substituted ferrocenyl chalcones using acetylferrocene (1) with different aldehydes (2a-2p) and comparing it with conventional method (CM). The synthesized compounds were characterized by various spectroscopic techniques viz IR, HR-MS, 1H NMR, and 13C NMR. The time required for completion of reaction in MM varied from 1 to 5 min as compared to CM which required 10–40 h. All the synthesized compounds were screened for antifungal activity against Sclerotium rolfsii and Alternaria solani. In vitro fungicidal activity revealed that compound 3o (ED50 = 23.24 mg L−1) was found to be most active against S. rolfsii. But in case of A. solani, compound 3c (ED50 = 29.9 mg L−1) showed highest activity. The nematicidal activity revealed that the compound 3b was more potent with LC50 values of 10.67, 7.30, and 4.55 ppm at 24, 48, and 72 h, respectively. 2D-Quantitative Structural Activity Relationship (2D-QSAR) analysis of these ferrocenyl chalcones was carried out by developing three different models namely Partial Least Squares (PLS, Model 1), Multiple Linear Regression (MLR, Model 2) and Principal Component Regression (PCR, Model 3). Statistical significance and predictive ability of these models were assessed by internal and external validation and also verified by leave one-out cross-validation. QSAR study revealed that MLR for S. rolfsii (r2 = 0.999, q2 = 0.996), PLS for A. solani (r2 = 0.934, q2 = 0.749) and PCR for M. incognita (r2 = 0.878, q2 = 0.772) were the best model. The physico-chemical parameters were calculated using VLife MDS 4.6 software. QSAR study could be employed for structure optimization to achieve better activity.
Highlights
Chalcones and their corresponding heterocyclic analogs were reported to exhibit several biological activities such as antibacterial, antifungal, insecticidal, nematicidal, anti-oxidant, antiplasmodial, antitumor, and anthelmintic due to occurrence of highly reactive unsaturated carbonyl moiety in skeleton (Vibhute and Baseer, 2003; Alam, 2004; Bag et al, 2009; Kalirajan et al, 2009; Shakil et al, 2010, 2011, 2013; Caboni et al, 2016)
Ferrocenyl chalcones were prepared by condensation of acetylferrocene with different benzaldehydes both by conventional and microwave methods
In microwave method (MM), reaction was completed in 1–5 min as compared to conventional method (CM) requiring 10–40 h (Table 1)
Summary
Chalcones and their corresponding heterocyclic analogs were reported to exhibit several biological activities such as antibacterial, antifungal, insecticidal, nematicidal, anti-oxidant, antiplasmodial, antitumor, and anthelmintic due to occurrence of highly reactive unsaturated carbonyl moiety in skeleton (Vibhute and Baseer, 2003; Alam, 2004; Bag et al, 2009; Kalirajan et al, 2009; Shakil et al, 2010, 2011, 2013; Caboni et al, 2016). HR-MS for C19H16FeO [M+H]+ m/z: Calcd 317.0623; Observed 317.0639 It was obtained as a red colored solid in 83% yield; m.p.:120– 122◦C, Rf: 0.50 (ethyl acetate: hexane, 1:4). SCHEME 2 | Method for the synthesis of 3p, ferrocenyl chalcones (Wu et al, 2002) It was obtained as an orange colored solid in 82% yield; m.p.:150– 152◦C, Rf: 0.28 (ethyl acetate: hexane, 1:4). HR-MS for C22H22FeO4 [M+H]+ m/z:Calcd 407.0940; Observed 407.0931 It was obtained as a dark red colored solid in 81% yield; m.p.:120– 122◦C, Rf: 0.37 (ethyl acetate: hexane, 1:4). HR-MS for C19H16FeO2 [M+H]+ m/z: Calcd 333.0572; Observed 333.0588 It was obtained as an orange colored solid in 82% yield; m.p.:140– 142◦C, Rf: 0.34 (ethyl acetate: hexane, 1:4). Unicolumn statistics was done to establish the accuracy of selection of training and test sets (Tables 2B, 3B, 4B) as maximum value of the training set was higher than that of the test set and the minimum value of the training set was lower than that of the test set
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