Asymmetric Total Synthesis of Pentacyclic Indole Alkaloid Andranginine and Absolute Configuration of Natural Product Isolated from Kopsia arborea

Ten-Step Total Synthesis of (-)-Andranginine

The total synthesis of the indole alkaloid (-)-andranginine has been achieved in 10 steps. Key reactions of the synthesis include a nucleophilic addition of acetylenyl anion to chiral N-sulfinyl imine, an intramolecular N-alkylation reaction to close the C ring, and a dienyne metathesis cascade reaction to construct the DE rings. Meanwhile, 16-epi-(-)-andranginine was also obtained with the developed strategy.

Highly Efficient Asymmetric Morita–Baylis–Hillman Reaction Promoted by Chiral Aziridine-Phosphines

Continuing our research on the use of organophosphorus derivatives of aziridines in asymmetric synthesis and expanding the scope of their applicability, chiral aziridine-phosphines obtained earlier in our laboratory were used as chiral catalysts in the asymmetric Morita–Baylis–Hillman reaction of methyl vinyl ketone and methyl acrylate with various aromatic aldehydes. The desired chiral products were formed in moderate to high chemical yields and with enantiomeric excess reaching value of 98% ee in some cases. The use of catalysts being pairs of enantiomers led to the desired products with opposite absolute configurations.

Recent Applications of the Diels–Alder Reaction in the Synthesis of Natural Products (2017–2020)

The Diels–Alder reaction has long been established as an extremely useful procedure in the toolbox of natural product chemists. It tolerates a wide spectrum of building blocks of different complexity and degrees of derivatization, and enables the formation of six-membered rings with well-defined stereochemistry. In recent years, many total syntheses of natural products have been reported that rely, at some point, on the use of a [4+2]-cycloaddition step. Among classic approaches, several modifications of the Diels–Alder reaction, such as hetero-Diels–Alder reactions, dehydro-Diels–Alder reactions and domino-Diels–Alder reactions, have been employed to extend the scope of this process in the synthesis of natural products. Our short review covers applications of the Diels–Alder reaction in natural product syntheses between 2017 and 2020, as well as selected methodologies which are inspired by, or that can be used to access natural products.

1 Introduction

2 Syntheses from 2017

3 Syntheses from 2018

4 Syntheses from 2019

5 Syntheses from 2020

6 Conclusion

Direct Conversion of 3-(2-Nitroethyl)-1H-Indoles into 2-(1H-Indol-2-yl)Acetonitriles

The recently discovered [4+1]-spirocyclization of nitroalkenes to indoles provided a convenient new approach to 2-(1H-indol-2-yl)acetonitriles. However, this reaction was complicated by the formation of inert 3-(2-nitroethyl)-1H-indole byproducts. Herein, we offer a workaround this problem that allows for effective transformation of the unwanted byproducts into acetonitrile target molecules.

Monoterpenoid indole alkaloids from the stems of Kopsia officinalis

Five new indole alkaloids, kopsiofficines H-L (1-5), along with fourteen known alkaloids (6-19) were isolated from the stems of Kopsia officinalis. Their structures were elucidated by extensive NMR, mass spectroscopic analyses and comparison to the reported data. All the isolated compounds were evaluated their anti-inflammatory activities by inhibiting IL-1β, PGE2 and TNF-α secretion in lipopolysaccharide (LPS)-activated RAW264.7 cells. Compounds 2, 3, 6, 7, 11, 12, 15, and 17 show significant anti-inflammatory activities. These results demonstrate pharmacodynamic substance basis of these folkloric claims.

Total Syntheses of Lycopodium and Monoterpenoid Indole Alkaloids Based on Biosynthesis-Inspired Strategies

The merits of biogenetic considerations in the chemical syntheses of natural products have been emphasized by describing the total syntheses of Lycopodium alkaloids; lycodine, flabellidine, lycopodine, and flabelliformine, as well as monoterpenoid indole alkaloids; C-mavacurine, kopsiyunnanine K, koumine, and 11-methoxy-19R-hydroxygelselegine.

Total synthesis of alkaloids using both chemical and biochemical methods

A chemoenzymatic approach to synthesize structurally complex natural alkaloids (tetrahydroisoquinoline antibiotics, indole diterpenes, and monoterpene indole alkaloids) has been reviewed.

Asymmetric Total Synthesis of Biphenylquinolizidine Alkaloids 4″-O-Demethyllythridine and 14-epi-4″-O-Demethyllythridine

The first asymmetric total synthesis of new biphenylquinolizidine alkaloids 4″-O-demethyllythridine and 14-epi-4″-O-demethyllythridine isolated from Heimia salicifolia was accomplished. The key steps in the synthesis were a copper(I)-catalyzed asymmetric intramolecular aza-Michael reaction to build a chiral 4-arylquinolizidine unit and an intramolecular Suzuki-Miyaura cross-coupling reaction to construct a macrolactone ring comprising a biphenyl moiety.

New otonecine-type pyrrolizidine alkaloid from Petasites japonicus

One new otonecine-type pyrrolizidine alkaloid secopetasitenine (1), along with petasitenine (fukinotoxine, 2), neopetasitenine (3), and senkirkine (4), was isolated from the whole plant of Petasites japonicus. The structure of 1 was determined by spectroscopic analyses and chemical conversion from the known alkaloid petasitenine (2).

The Baylis–Hillman reaction: a new continent in organic chemistry – our philosophy, vision and over three decades of research

This mini review describes in brief the way in which our research has contributed towards the development of the Baylis–Hillman reaction as a powerful tool in synthetic chemistry, offering unending opportunities and intellectual challenges to understand and address the present day requirements in the area of organic chemistry.