Insecticidal and fungicidal activity of new synthesized chitosan derivatives

Abstract

Chitosan, the N-deacetylated derivative of chitin, is a potential biopolysaccharide owing to its specific structure and properties. In this paper, we report on the synthesis of 24 new chitosan derivatives, N-alkyl chitosans (NAC) and N-benzyl chitosans (NBC), that are soluble in dilute aqueous acetic acid. The different derivatives were synthesized by reductive amination and analyzed by 1H NMR spectroscopy. A high degree of substitution (DS) was obtained with N-(butyl)chitosan (DS 0.36) at a 1:1 mole ratio for NAC derivatives and N-(2,4-dichlorobenzyl)chitosan (DS 0.52) for NBC derivatives. Their insecticidal and fungicidal activities were tested against larvae of the cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), the grey mould Botrytis cinerea Pers (Leotiales: Sclerotiniaceae) and the rice leaf blast Pyricularia grisea Cavara (Teleomorph: Magnaporthe grisea (Hebert) Barr). The oral feeding bioassay indicated that all the derivatives had significant insecticidal activity at 5 g kg(-1) in artificial diet. The most active was N-(2-chloro-6-fluorobenzyl)chitosan, which caused 100% mortality at 0.625 g kg(-1), with an estimated LC50 of 0.32 g kg(-1). Treated larvae ceased feeding after 2-3 days; the mechanism of action remains unknown. In a radial hyphal growth bioassay with both plant pathogens, all derivatives showed a higher fungicidal action than chitosan. N-Dodecylchitosan, N-(p-isopropylbenzyl)chitosan and N-(2,6-dichlorobenzyl)chitosan were the most active against B cinerea, with EC50 values of 0.57, 0.57 and 0.52 g litre(-1), respectively. Against P grisea, N-(m-nitrobenzyl)chitosan was the most active, with 77% inhibition at 5 g litre(-1). The effect of different substitutions is discussed in relation to insecticidal and fungicidal activity.

Insecticidal activity of chitosans of different molecular weights and chitosan-metal complexes against cotton leafworm Spodoptera littoralis and oleander aphid Aphis nerii

“…Previous studies on the biological activity of chitosan and its derivatives against S. littoralis reported that the unmodified chitosan showed low insecticidal activity against larvae of S. littoralis, but its chemical modification led to an increase in the activity Rabea et al 2005Rabea et al , 2006Badawy 2008). Bioassays with 17 derivatives of N-(alkyl) chitosans at a rate of 5 g/kg diet demonstrated that N- (propyl) chitosan, N-(undecanyl) chitosan and N-(3-phenylpropyl) chitosan strongly inhibited larval weight gain in S. littoralis, with respective reductions of 77 and 65% after 4 days of feeding (Rabea et al 2006).…”

Chemically modified chitosans as antimicrobial agents against some plant pathogenic bacteria and fungi

“…Low-molecular-weight chitosan (made from coarse ground crab, 89% degree of deacetylation) was supplied by Sigma-Aldrich Co. (St. Louis, USA). Eight chemically modified chitosan derivatives, listed below in Figure 1, were prepared and characterized as described by Rabea et al (2005). The compounds with the indicated functional groups and different substituents were the following: compound 1, N-(p-chlorobenzyl)chitosan, compound 2, N- (o-chlorobenzyl)chitosan, compound 3, N-(p-fluorobenzyl)-chitosan, compound 4, N-(o-fluorobenzyl) chitosan, compound 5, N-(o,p-dichlorobenzyl)chitosan, compound 6, N-(o,o-dichlorobenzyl)chitosan, compound 7, N-(o,o-difluorobenzyl)chitosan and compound 8, N-(o-chloro,o-fluorobenzyl …”

“…N-(o,o-dichlorobenzyl)-chitosan within a series of N-(benzyl)chitosan derivatives was the most active compound against b. cinerea with EC 50 of 520 mg/l (Rabea et al 2005). In addition, N- (o,p-diethoxybenzyl) (Rabea et al 2009).…”

“…Recently, some of N-substituted chitosan derivatives were synthesised and their biological activities were evaluated against some plant pathogenic fungi including botrytis cinerea, Pyricularia grisea, F. oxysporum, and P. debaryanum (Rabea et al 2005(Rabea et al , 2009Badawy 2008Badawy , 2010. N-(o,o-dichlorobenzyl)-chitosan within a series of N-(benzyl)chitosan derivatives was the most active compound against b. cinerea with EC 50 of 520 mg/l (Rabea et al 2005).…”

A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields

“…Chitosan has been found to show strong insecticidal activity in some plant pests [45]. Rabea et al [45] found that a chitin derivative (N-(2-chloro-6-fluorobenzyl-chitosan) caused 100% mortality of larvae of the cotton leafworm (Spodoptera littoralis) that consumed it when incorporated into an artificial diet at 5 g kg −1 .…”