One-pot chemo- and photo-enzymatic linear cascade processes

The combination of chemo- and photocatalyses with biocatalysis, which couples the flexible reactivity of the photo- and chemocatalysts with the highly selective and environmentally friendly nature of enzymes in one-pot linear cascades, represents a powerful tool in organic synthesis. However, the combination of photo-, chemo- and biocatalysts in one-pot is challenging because the optimal operating conditions of the involved catalyst types may be rather different, and the different stabilities of catalysts and their mutual deactivation are additional problems often encountered in one-pot cascade processes. This review explores a large number of transformations and approaches adopted for combining enzymes and chemo- and photocatalytic processes in a successful way to achieve valuable chemicals and valorisation of biomass. Moreover, the strategies for solving incompatibility issues in chemo-enzymatic reactions are analysed, introducing recent examples of the application of non-conventional solvents, enzyme-metal hybrid catalysts, and spatial compartmentalization strategies to implement chemo-enzymatic cascade processes.

Late-stage Modification of Cage Diones by Tandem Metathesis

Herein, we report the application of tandem ring-opening cross-metathesis (ROCM) and tandem ring-opening cross-metathesis followed by cross-metathesis (ROCM/CM) in highly strained diastereomeric heptacyclic cage diones (HCCD's) catalyzed by ruthenium catalysts. These caged diastereomeric compounds have a high degree of ring strain as well as steric congestion. Therefore, the present work related to ROCM is unique and intricate as compared to simple norbornene derivatives. It is useful to prepare new hexacyclic cage derivatives suitable for high-energy density materials. The synthetic strategy of starting cage compounds features the Diels-Alder reaction, and [2+2] photocycloaddition as key steps.

The simplest Diels-Alder reactions are not endo-selective

There is a widespread perception that the high level of endo selectivity witnessed in many Diels-Alder reactions is an intrinsic feature of the transformation. In contrast to expectations based upon this existing belief, the first experimental Diels-Alder reactions of a novel, deuterium-labeled 1,3-butadiene with commonly used mono-substituted alkenic dienophiles (acrolein, methyl vinyl ketone, acrylic acid, methyl acrylate, acrylamide and acrylonitrile) reveal kinetic endo : exo ratios close to 1 : 1. Maleonitrile, butenolide, α-methylene γ-butyrolactone, and N-methylmaleimide behave differently, as does methyl vinyl ketone under Lewis acid catalysis. CBS-QB3 calculations incorporating solvent and temperature parameters give endo : exo product ratios that are in near quantitative agreement with these and earlier experimental findings. This work challenges the preconception of innate endo-selectivity by providing the first experimental evidence that the simplest Diels-Alder reactions are not endo-selective. Trends in behaviour are traced to steric and electronic effects in Diels-Alder transition structures, giving new insights into these fundamental processes.

Diels–Alder reactions between cyclopentadiene analogs and benzoquinone in water and their application in the synthesis of polycyclic cage compounds

Diels–Alder reactions between cyclopentadiene analogs and p-benzoquinone were explored in water and yielded 83–97% product, higher than the results reported in water with a catalyst or cetrimonium bromide (CTAB) micelles. The novel adduct 10 was synthesized and further used to synthesize the bi-cage hydrocarbon 4,4′-spirobi[pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane], which has a high density (1.2663 g cm⁻³) and a high volumetric heat of combustion (53.353 MJ L⁻¹). Four novel bi-cage hydrocarbon compounds were synthesized in water using this method starting from 2,2′-bi(p-benzoquinone) and cyclopentadiene analogs.

Diels–Alder reactions between cyclopentadiene analogs and p-benzoquinone were explored in water and yielded 83–97% product, higher than the results reported in water with a catalyst or cetrimonium bromide (CTAB) micelles.

Design and synthesis of propellane derivatives and oxa-bowls via ring-rearrangement metathesis as a key step

Various intricate propellane derivatives and oxa-bowls have been synthesized via a ring-rearrangement metathesis (RRM) as a key step starting from readily accessible starting materials such as p-benzoquinone, 1,4-naphthoquinone and 1,4-anthraquinone.

New 1,4-anthracenedione derivatives with fused heterocyclic rings: synthesis and biological evaluation

New 1,4-anthracenediones bearing fused-heterocycle rings were synthesized and evaluated as cytotoxics, antifungals and antivirals. Some of them showed GI₅₀ at the μM level.

Synthesis of the 2-methylene analogue of the HRV 3C protease inhibitor thysanone (2-carbathysanone)

The Human Rhinovirus (HRV) is the major aetiological agent for the common cold, for which only symptomatic treatment is available. HRV maturation and replication is entirely dependent on the activity of a virally encoded 3C protease that represents an attractive target for the development of therapeutics to treat the common cold. Herein we report the synthesis and biological evaluation of the 2-methylene analogue of the HRV 3C protease inhibitor (-)-thysanone (1) namely 2-carbathysanone (2), in an attempt to decipher the structural features in the natural product that are responsible for the 3C protease activity. 2-Carbathysanone (2) (and related analogues (±)-cis-23, (±)-cis-30, (±)-31) did not inhibit HRV 3C protease, indicating that the lactol functionality present in (-)-thysanone (1) is a critical structural feature required for inhibition.