Pestalotiopsin A. Enantioselective Construction of Potential Building Blocks Derived from Antipodal Cyclobutanol Intermediates

Caryophyllene Sesquiterpenes from a Chaetomium globosum Endophyte of the Canadian Medicinal Plant Empetrum nigrum

Punctaporonins T (1) and U (2), new caryophyllene sesquiterpenes, were isolated with three known punctaporonins, A (3), B (4), and C (5), from the endophytic fungus Chaetomium globosum (TC2-041). The structures and relative configurations of punctaporonins T and U were elucidated based on a combination of HRESIMS, 1D/2D NMR spectroscopic analysis, and X-ray diffraction analysis, while their absolute configuration is presumed to be consistent with the co-isolated 3-5 on biogenetic arguments. Compound 1 showed weak inhibitory activity against both Mycobacterium tuberculosis and Staphylococcus aureus.

Recent advances in the synthesis of gem-dimethylcyclobutane natural products

Covering: January 2000 to July 2018 gem-Dimethylcyclobutanes are a common motif found in a multitude of natural products, and thus these structures have captivated synthetic chemists for years. However, until the turn of the century, most synthetic efforts relied upon the use of widely available terpenes, such as pinene or caryophyllene, that already contain the gem-dimethylcyclobutane motif. This approach limits the scope of molecules that can be accessed readily. This review highlights recent syntheses in which the gem-dimethylcyclobutane is assembled via de novo approaches. An outlook on the future of this research area is also provided.

Domino 1,4- and 1,6-Addition Reactions of Ketene Silyl Acetals to Dialkynyl Imines Promoted by Aluminum Chloride: Synthesis of Multifunctionalized β-Lactams

Domino 1,4- and 1,6-addition reactions of ketene silyl acetals to dialkynyl imines are disclosed. Aluminum chloride promoted domino 1,4- and 1,6-addition reactions of ketene silyl acetals to dialkynyl imines to give a variety of alkenyl iminocyclobutenones in moderate to good yields. The chemoselective reduction of alkenyl iminocyclobutenones and the subsequent thermal rearrangement of resulting alkenyl aminocyclobutenones in the presence of appropriate amines provided cis or trans multifunctionalized β-lactams in moderate to high yields with good to high diastereoselectivities.

Novel macrocyclic molecules based on 12a-N substituted 16-membered azalides and azalactams as potential antifungal agents

Novel macrocyclic molecules comprising sulfonyl and acyl moiety at the position N-12a of 16-membered azalides (6a-n) and azalactams (10a-r) scaffold were synthesized from cyclododecanone 1 as starting material via 5 steps and 4 steps, respectively. The antifungal activity of these compounds against Sclerotinia sclerotiorum, Pyricularia oryzae, Botrytis cinerea, Rhizoctonia solani and Phytophthora capsici were evaluated and found that compounds possessing α-exomethylene (6c, 6d, 6e and 6g) showed antifungal activity comparable to commercial fungicide Chlorothalonil against P. oryzae and compounds possessing p-chlorobenzoyl exhibited enhanced antifungal activity than those with other substituents against S. sclerotiorum, P. oryzae, and B. cinerea. These findings suggested that the α-exomethylene and p-chlorobenzoyl may be two potential pharmacological active groups with antifungal activities.

Total syntheses of (+)- and (-)-pestalotiopsin A

An enantioselective total synthesis of both enantiomers of caryophyllene-type sesquiterpenoid pestalotiopsin A has been achieved, thereby establishing the absolute stereochemistry of natural (+)-pestalotiopsin A. Highlights of the synthesis include a [2 + 2] cycloaddition of N-propioloyl Oppolzer's camphorsultam and ketene dialkyl acetal and subsequent highly stereoselective 1,4-hydride addition/protonation, an aldol reaction of functionalized bicyclic lactone with aldehyde, an efficient intramolecular Nozaki-Hiyama-Kishi (NHK) reaction for the construction of the highly strained (E)-cyclononene ring, and a palladium-catalyzed reduction of allylic mesylate with retention of the E configuration.

Pestalotiopsin A. Side chain installation and exhaustive probing of olefin metathesis as a possible tool for elaborating the cyclononene ring

A program directed toward an asymmetric synthesis of pestalotiopsin A is described. The routing begins with the dextrorotatory cyclobutanol 37, which is combined with the enantiomerically defined building blocks ent-15 and 16. These units are incorporated via stereocontrolled 1,2-nucleophilic addition and anti-aldol coupling, respectively. With these straightforward reactions accomplished, the sequel involved the introduction of terminal double bonds in anticipation of the fact that the (E)-cyclononene substructure could be realized by ring-closing metathesis. This central issue was evaluated with several diene substrates and catalysts, all to no avail. Cross-metathesis experiments involving 59 and 65 with the functionalized heptene 60 revealed a marked difference in the inability to engage interaction with the ruthenium catalyst. This awkwardness could not be skirted.