5- Methoxy-3-pyrrolin-2-one

Although terrestrial cyanobacteria are well-recognized producers of a wide range of bioactive compounds, marine species have received less attention until recently [159]. One of the most abundant and studied marine cyanobacteria is the pantropic Lyngbya majuscula (Oscillatoriaceae). A prolific producer of metabolites, it has so far yielded more than 110 secondary metabolites including compounds that exhibit antiproliferative, immunosuppressants, antifeedant and molluscidal activities [159,160]. Shallow water varieties of the cyanophyte contain N-substituted amides of 75-methoxytetradec-4E-enoic acid and of 7S-methoxy-9-methylhexa-dec-4 -enoic acid called malyngamides, a sub-class of which contains the 4-methoxy-3-pyrrolin-2-one system [158]. 

Sorangium cellulosum is an ubiquitous soil bacterium that belongs to the order Myxococcales. It has the ability to glide over solid surfaces, to live in a biofilm and form fruiting bodies. Members of this taxon are a particularly rich source of metabolites with remarkable biological activities [177]. From one strain, another example of N-acyl-4-methoxy-3-pyrrolin-2-ones has been isolated. Eliamid (110) has been claimed to have cytostatic, nematocidal and fungicidal activities [178]. 

Intermolecular addition of carbon nucleophiles to the ri2-pyrrolium complexes has shown limited success because of the decreased reactivity of the iminium moiety coupled with the acidity (pKa 18-20) of the ammine ligands on the osmium, the latter of which prohibits the use of robust nucleophiles. Addition of cyanide ion to the l-methyl-2//-pyr-rolium complex 32 occurs to give the 2-cyano-substituted 3-pyrroline complex 75 as one diastereomer (Figure 15). In contrast, the 1-methyl-3//-pyrrolium species 28, which possesses an acidic C-3-proton in an anti orientation, results in a significant (-30%) amount of deprotonation in addition to the 2-pyrroline complex 78 under the same reaction conditions. Uncharacteristically, 78 is isolated as a 3 2 ratio of isomers, presumably via epimerization at C-2.17 Other potential nucleophiles such as the conjugate base of malononitrile, potassium acetoacetate, and the silyl ketene acetal 2-methoxy-l-methyl-2-(trimethylsiloxy)-l-propene either do not react or result in deprotonation under ambient conditions. 

Very recently it was found that when carrying out the photo-oxidation in methanol, pyrrole gives mainly 19d and a low yield of maleimide.28a Similarly, 3,4-diethylpyrrole gives diethylmaleimide as the main product with minor quantities of 3,4-diethyl-5-methoxy-id3-pyrrolin-2-one (19e). No maleimide was found when photo-oxidation was performed in aqueous solution. 

The direct reaction between diketene and 2-methoxy-l-pyrroline (449) gave a mixture of 450 (11%) and 8a-methoxy-2-methyleneperhydropyr-rolo[2,l-Z>][l,3]oxazin-4-one (451, 73%) (75H927). 

Other types of tetramic acid derivatives are A-acyl-4-methoxy-3-pyrrolin-2-ones or 4-O-methyl ethers of A-acylated tetramic acids. The only metabolites of this type containing a dienic structure are pukeleimides A (87), G (88), B (89) and F (90). They are nontoxic compounds isolated from the marine cyanophyte Lyngbya majuscula [158], a blue-green algae. 

Padwa and coworkers realized the synthesis of 2,4-disubstituted pyrroles using rearrangements of 2-fiiranyl carbamates via 5-methoxy-3-pyrrolin-2-one intermediates. 2-Furanyl carbamate 593 was treated with iodine and sodium bicarbonate followed by methyl iodide and silver oxide to give the N-substituted 5-methoxy-3-pyrrolin-2-one 595 via the iodinated intermediate 594 (Scheme 173 20090L1233). Padwa employed this method to synthesize 5-methoxypyrrol-2-ones, which were then treated with alkyl hthiates to give tricycHc products (2009T6720). 

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