Pyrrolizidine alkaloids

Robertson, Jeremy; Stevens, Kiri

doi:10.1039/c4np00055b

Cited by 156 publications

(92 citation statements)

References 259 publications

(237 reference statements)

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“…Other compounds such as Pyrroles (Pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-) are commonly found in various Streptomyces species (Robertson and Stevens, 2014; Ser et al, 2015b, 2016b,c; Tan et al, 2015; Awla et al, 2016). Furthermore, Pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(phenylmethyl) was found to be able to protect plants from phytopathogenic fungi (Zhou et al, 2015).…”

Section: Streptomyces Spp As Biocontrol Agents Against M Oryzaementioning

confidence: 99%

The Potential of Streptomyces as Biocontrol Agents against the Rice Blast Fungus, Magnaporthe oryzae (Pyricularia oryzae)

et al. 2017

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Rice is a staple food source for more than three billion people worldwide. However, rice is vulnerable to diseases, the most destructive among them being rice blast, which is caused by the fungus Magnaporthe oryzae (anamorph Pyricularia oryzae). This fungus attacks rice plants at all stages of development, causing annual losses of approximately 10–30% in various rice producing regions. Synthetic fungicides are often able to effectively control plant diseases, but some fungicides result in serious environmental and health problems. Therefore, there is growing interest in discovering and developing new, improved fungicides based on natural products as well as introducing alternative measures such as biocontrol agents to manage plant diseases. Streptomyces bacteria appear to be promising biocontrol agents against a wide range of phytopathogenic fungi, which is not surprising given their ability to produce various bioactive compounds. This review provides insight into the biocontrol potential of Streptomyces against the rice blast fungus, M. oryzae. The ability of various Streptomyces spp. to act as biocontrol agents of rice blast disease has been studied by researchers under both laboratory and greenhouse/growth chamber conditions. Laboratory studies have shown that Streptomyces exhibit inhibitory activity against M. oryzae. In greenhouse studies, infected rice seedlings treated with Streptomyces resulted in up to 88.3% disease reduction of rice blast. Studies clearly show that Streptomyces spp. have the potential to be used as highly effective biocontrol agents against rice blast disease; however, the efficacy of any biocontrol agent may be affected by several factors including environmental conditions and methods of application. In order to fully exploit their potential, further studies on the isolation, formulation and application methods of Streptomyces along with field experiments are required to establish them as effective biocontrol agents.

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Section: Streptomyces Spp As Biocontrol Agents Against M Oryzaementioning

confidence: 99%

The Potential of Streptomyces as Biocontrol Agents against the Rice Blast Fungus, Magnaporthe oryzae (Pyricularia oryzae)

et al. 2017

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“…In addition, perfect chemoselective functionalization of an alkyl bromide in the presence of a primary chloroalkane was observed ( 16 , 96% yield). A deprotection-cyclization sequence with this material would provide rapid access to the bicyclic tertiary amine core of the naturally occurring pyrrolizidine alkaloids 31 . The presence of free hydroxyl groups is fully compatible with the iridium photocatalyst and the nickel complex ( 17 , 86% yield).…”

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confidence: 99%

Metallaphotoredox-catalysed sp3–sp3 cross-coupling of carboxylic acids with alkyl halides

Johnston

Smith

Allmendinger

et al. 2016

Nature

398

207

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Over the last half-century, transition metal-mediated cross-coupling reactions have changed the way in which complex organic molecules are synthesized. Indeed, the predictable and chemoselective nature of these transformations has led to their widespread adoption across a vast array of chemical research areas1. However, the construction of sp3–sp3 bonds, a fundamental unit of organic chemistry, remains an important yet elusive objective for cross-coupling reaction engineering2. In comparison to related procedures with sp2-hybridized species, the development of methods for sp3–sp3 bond formation via transition metal catalysis has been historically hampered by deleterious side-reactions, such as β-hydride elimination with Pd-catalysis, and the reluctance of alkyl halides to undergo oxidative addition3,4. To address this issue, a number of research groups have demonstrated the feasibility of nickel-catalyzed cross-coupling processes to form sp3–sp3 bonds that utilize organometallic nucleophiles and alkyl electrophiles5–7. In particular, the coupling of alkyl halides with pregenerated organozinc8–10, Grignard11,12, and organoborane13 species has been used to furnish diverse molecular structures. However, the poor step and atom economies along with the operational difficulties associated with making, carrying, and using these sensitive coupling partners has hindered their widespread adoption. The prospect of establishing a generically useful sp3–sp3 coupling technology that employs bench-stable, native organic functional groups, without the need for pre-functionalization or substrate derivatization, would therefore be a valuable addition to fields of research that rely on organic molecule construction. Here, we demonstrate that the synergistic merger of photoredox and nickel catalysis enables the direct formation of sp3–sp3 bonds using only simple carboxylic acids and alkyl halides as the nucleophilic and electrophilic coupling partners, respectively. The outlined protocol is suitable for a wide array of primary and secondary carboxylic acids and does not require the presence of radical stabilizing groups. The merit of this coupling strategy is illustrated by the expedient synthesis of the pharmaceutical tirofiban in four steps from commercially available starting materials.

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“…[15,16] However,their synthesis usually requires many steps or reagents,t he preparation of complex substrates,s uffers from severe substrate limitations and/or requires harsh reaction conditions. [15,16] However,their synthesis usually requires many steps or reagents,t he preparation of complex substrates,s uffers from severe substrate limitations and/or requires harsh reaction conditions.…”

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confidence: 99%

Photooxygenation of Furylalkylamines: Easy Access to Pyrrolizidine and Indolizidine Scaffolds

et al. 2016

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Ahighly adaptable method targeting the ubiquitous and very important pyrrolizidine and indolizidine scaffolds is presented. The general synthetic utility of the method is underscored by its application to the rapid and easy synthesis of five natural products starting from readily accessible alkylfuran precursors.T hese unprotected primary furylalkylamines are subjected to photooxygenation conditions,w hich initiate ac omplex cascade reaction sequence concluding with the production of high value motifs.T his sequence can be tailored to need by varying the choice of both photosensitizer and base additive.

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Pyrrolizidine alkaloids

Abstract: This review covers pyrrolizidine alkaloids isolated from natural sources. Topics include: aspects of structure, isolation, and biological/pharmacological studies; total syntheses of necic acids, necine bases and closely-related non-natural analogues.

Cited by 156 publications

References 259 publications

The Potential of Streptomyces as Biocontrol Agents against the Rice Blast Fungus, Magnaporthe oryzae (Pyricularia oryzae)

The Potential of Streptomyces as Biocontrol Agents against the Rice Blast Fungus, Magnaporthe oryzae (Pyricularia oryzae)

Metallaphotoredox-catalysed sp3–sp3 cross-coupling of carboxylic acids with alkyl halides

Photooxygenation of Furylalkylamines: Easy Access to Pyrrolizidine and Indolizidine Scaffolds

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