Stereocontrolled Total Synthesis of Nonenolide

Steglich esterification: A versatile synthetic approach toward the synthesis of natural products, their analogues/derivatives

The exploitation of natural products and their analogues in the field of pharmacology has been regarded as of great importance. It can be attributed to the fact that these scaffolds exhibit diverse chemical properties, distinct biological activities and zenith specificity in their biochemical processes, enabling them to act as favorable structures for lead compounds. The synthesis of natural products has been a crafty and hard-to-achieve task. Steglich esterification reaction has played a significant role in that area. It is a mild and efficient technique for constructing ester linkages. This technique involves the establishment of ester moiety via a carbodiimide-based condensation of a carboxylic acid with an alcohol, thiol or an amine catalyzed by dimethyl aminopyridine (DMAP). Specifically, labile reagents with multiple reactive sites are esterified efficiently with the classical and modified Steglich esterification conditions, which accounts for their synthetic utility. This review encloses the performance of the Steglich esterification reaction in forging the ester linkage for executing the total synthesis of natural products and their derivatives since 2018.

Total Synthesis of Kadcoccinic Acid A Trimethyl Ester

The first total synthesis of the trimethyl ester of kadcoccinic acid A is described. The central structural element of our synthesis is a cyclopentenone motif that allows the assembly of the natural product skeleton. A gold(I)-catalyzed cyclization of an enynyl acetate led to efficient construction of the cyclopentenone scaffold. In this step, optimization studies revealed that the stereochemistry of the enynyl acetate dictates regioisomeric cyclopentenone formation. The synthesis further highlights an efficient copper-mediated conjugate addition, merged with a gold(I)-catalyzed Conia-ene reaction to connect the two fragments, thereby forging the D-ring of the natural product. The synthetic strategy reported herein can provide a general platform to access the skeleton of other members of this family of natural products.

Two New Nonenolides from Diaporthe sp. SXZ-19, an Endophytic Fungus of Camptotheca Acuminata

Two new nonenolides named diaportheolides A (1) and B (2) were isolated from the endophytic fungus Diaporthe sp. SXZ-19 of Camptotheca acuminata. The chemical structures of 1 and 2 were elucidated by spectroscopic analyses, including 1D- and 2D-NMR experiments and HR-ESI-MS data analysis. Their in vitro antibacterial activities are established to be insignificant.

The Role of Total Synthesis in Structure Revision and Elucidation of Decanolides (Nonanolides)

Ten-membered lactones are commonly observed structures of natural products. They are mostly fungal metabolites, which often act as plant pathogens, but recently ten-membered lactones were identified as pheromones of frogs and termites. Although modern spectroscopic methods are nowadays routinely used to elucidate the structure of natural products, structural assignments of ten-membered lactones often remain incomplete or are surprisingly often erroneous. Most errors concern the absolute configuration. The examples discussed in this chapter demonstrate that enantioselective total synthesis is not only an efficient tool for corroborating or revising a proposed structure, but that the synthesis of different stereoisomers as references for gas chromatographic investigations can be a vital part of the structure elucidation process if only minute amounts of material are available. As a method of outstanding importance for the synthesis of ten-membered lactones olefin metathesis has emerged. Most of the examples discussed herein use one or more olefin metathesis reactions as key steps.

Identification and Enantiodivergent Synthesis of (5 Z,9 S)-Tetradec-5-en-9-olide, a Queen-Specific Volatile of the Termite Silvestritermes minutus

The queens of social insects differ from sterile colony members in many aspects of their physiology. Besides adaptations linked with their specialization for reproduction and extended lifespan, the queens also invest in the maintenance of their reproductive dominance by producing exocrine chemicals signaling their presence to the nestmates. The knowledge of the chemistry of queen-specific cues in termites is scarce. In addition to the contact recognition based on cuticular hydrocarbons, long-range signals mediated by volatiles are expected to participate in queen signaling, especially in populous colonies of higher termites (Termitidae). In queens of the higher termite Silvestritermes minutus (Syntermitinae), we have detected a previously undescribed volatile. It is present in important quantities on the body surface and in the headspace, ovaries, and body cavity. MS and GC-FTIR data analyses led us to propose the structure of the compound to be a macrolide 10-pentyl-3,4,5,8,9,10-hexahydro-2 H-oxecin-2-one. We performed enantiodivergent syntheses of two possible enantiomers starting from enantiopure ( S)-glycidyl tosylate. The synthetic sequence involved macrolide-closing metathesis quenched with a ruthenium scavenging agent. The absolute and relative configuration of the compound was assigned to be (5 Z,9 S)-tetradec-5-en-9-olide. Identification and preparation of the compound allow for investigation of its biological significance.