A short, efficient, and stereoselective total synthesis of a pyrrolidine alkaloid: (-)-codonopsinine

Synthesis of Macrolactone Core of ent-Formosalide A via Regioselective Ether Cyclization

Formosalide A is a cytotoxic macrolide isolated from the dinoflagellate Prorocentrum sp, whose structure is characterized by functionalized 5- and 6-membered ether rings embedded in the macrolactone and an all cis-tetraene side chain. Here, we report the synthesis of the macrolactone core of ent-formosalide A. Our approach is highlighted by the Au-mediated 6-exo-dig cyclization for the synthesis of the 6-membered ether ring, which proceeded in a highly regioselective manner. Control experiments demonstrated that the acyclic protecting group of the C9,C10-diol was crucial for the desired 6-exo-dig cyclization. Theoretical studies were performed focusing on structural component analysis, which suggested that the C8-C9-C10-C11 dihedral angle induced by the protecting group controlled the regioselectivity. An additional 6 steps including Shiina macrolactone formation from the 6-membered ether ring completed the synthesis of the macrolactone core of ent-formosalide A.

Sharpless Asymmetric Dihydroxylation: An Impressive Gadget for the Synthesis of Natural Products: A Review

Sharpless asymmetric dihydroxylation is an important reaction in the enantioselective synthesis of chiral vicinal diols that involves the treatment of alkene with osmium tetroxide along with optically active quinine ligand. Sharpless introduced this methodology after considering the importance of enantioselectivity in the total synthesis of medicinally important compounds. Vicinal diols, produced as a result of this reaction, act as intermediates in the synthesis of different naturally occurring compounds. Hence, Sharpless asymmetric dihydroxylation plays an important role in synthetic organic chemistry due to its undeniable contribution to the synthesis of biologically active organic compounds. This review emphasizes the significance of Sharpless asymmetric dihydroxylation in the total synthesis of various natural products, published since 2020.

Synthesis of the Hexahydropyrrolo-[3,2-c]-quinoline Core Structure and Strategies for Further Elaboration to Martinelline, Martinellic Acid, Incargranine B, and Seneciobipyrrolidine

Natural products are rich sources of interesting scaffolds possessing a plethora of biological activity. With the isolation of the martinella alkaloids in 1995, namely martinelline and martinellic acid, the pyrrolo[3,2-c]quinoline scaffold was discovered. Since then, this scaffold has been found in two additional natural products, viz. incargranine B and seneciobipyrrolidine. These natural products have attracted attention from synthetic chemists both due to the interesting scaffold they contain, but also due to the biological activity they possess. This review highlights the synthetic efforts made for the preparation of these alkaloids and formation of analogues with interesting biological activity.

Design and total synthesis of (-)-codonopsinine, (-)-codonopsine and codonopsinine analogues by O-(2-oxopyrrolidin-5-yl)trichloroacetimidate as amidoalkylating agent with improved antimicrobial activity via solid lipid nanoparticle formulations

A general strategy towards total synthesis of (-)-codonopsinine, (-)-codonopsine and codonopsinine analogues has been developed from (D)-tartaric acid via the intermediate (3S,4R)-1-methyl-2-oxo-5-(2,2,2-trichloroacetamido)pyrrolidinediacetate (7). α-amidoalkylation studies of 7 with electron rich benzene derivative 8a-g as C-nucleophiles afforded (aryl derivatives) 9a-g. The target compounds 1, 2 and 13c-g were readily obtained from 10a-gvia Grignard addition to the homochiral lactam which was produced by deoxygenation using Lewis-acid followed by deacetylation. The synthesized compounds were loaded onto solid lipid nanoparticle formulations (SLNs) prepared by hot emulsification-ultrasonication technique using Compritol as solid lipid and Pluronic f68 as surfactant. SLNs were fully evaluated and the permeation of synthesized compound from SLNs was assayed against non-formulated compounds through dialysis membranes using Franz cell. The data indicated good physical characteristics of the prepared SLNs, sustaining of release profiles and significant improvement of permeation ability when compared to the non-formulated compounds. The antibacterial and antifungal activities of 1, 2 and 13c-g were determined by disc diffusion and microbroth dilution method to determine the minimum inhibitory concentrations (MIC) against seven microorganisms (Staphyloccus aureus, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacter baumannii and Candida albicans). The most active compounds against the Gram positive S. aureus were 1, 13C, 13d, and 13g. Also, 13c, 13d, and 13e had antibacterial activity but not 13f against some Gram negative organisms (E. coli, and P. mirabilis). MIC concentrations against P. aeruginosa, and K. pneumoniae were ≥512 μg/ml, while that against A. baumannii was ≥128 μg/ml except for nanoformulae of 13e and 13f that were 16 and 64 μg/ml, respectively. No antifungal activity against Candida albicans was recorded for all compounds and their nanoformulae (MIC > 1024 μg/ml). SLNs were found to decrease the MIC values for some of the compounds with no effect on the antifungal activity. In conclusion, we demonstrated a novel, straight-forward and economical procedure for the total synthesis of (-)-codonopsinine 1, (-)-codonopsine 2 and codonopsinine analogues 13c-g from simple and commercially available starting materials; d-tartaric acid; with antimicrobial activities against Gram positive and Gram-negative organisms that were improved by SLNs formulations.

Total Synthesis and Absolute Stereochemical Assignment of Microgrewiapine A and Its Stereoisomers

Total synthesis of both enantiomers of (-)-(2 S,3 R,6 S)- and (+)-(2 R,3 S,6 R)-microgrewiapine A along with (+)-microcosamine A and (-)-6- epi-microgrewiapine A from chiral 1-(α-methylbenzyl)-aziridine-2-carboxylate was accomplished for the first time. Key steps involved in this synthesis include one-pot reductive ring-opening of aziridine, debenzylation, intramolecular N-alkylation to obtain the key piperidine ring, and Julia-Kociensky olefination. The absolute configuration of natural microgrewiapine A is assigned as (+)-(2 R,3 S,6 R), which is opposite to the originally proposed structure by comparing optical rotation data of both synthetic enantiomers.

In vitro inhibitory and cytotoxic activity of MFM 501, a novel codonopsinine derivative, against Methicillin-Resistant Staphylococcus aureus clinical isolates

28 new pyrrolidine types of compounds as analogues for natural polyhydroxy alkaloids of codonopsinine were evaluated for their anti-MRSA activity using MIC and MBC value determination assay against a panel of S. aureus isolates. One pyrrolidine compound, MFM 501, exhibited good inhibitory activity with MIC value of 15.6 to 31.3 μg/mL against 55 S. aureus isolates (43 MRSA and 12 MSSA isolates). The active compound also displayed MBC values between 250 and 500 μg/mL against 58 S. aureus isolates (45 MRSA and 13 MSSA isolates) implying that MFM 501 has a bacteriostatic rather than bactericidal effect against both MRSA and MSSA isolates. In addition, MFM 501 showed no apparent cytotoxicity activity towards three normal cell lines (WRL-68, Vero, and 3T3) with IC₅₀ values of >625 µg/mL. Selectivity index (SI) of MFM 501 gave a value of >10 suggesting that MFM 501 is significant and suitable for further in vivo investigations. These results suggested that synthetically derived intermediate compounds based on natural products may play an important role in the discovery of new anti-infective agents against MRSA.

Copper-catalyzed tandem oxidation-olefination process

A novel catalytic sequence aerobic oxidation-olefination has been developed. A single and inexpensive copper catalyst provides a large range of olefins from alcohols in good to excellent yields. The reaction exhibits excellent functional group compatibility, and the nonbasic reaction conditions allow the transformation of chiral substrates without racemization.