A practical and scaleable total synthesis of the jaborandi alkaloid (+)-pilocarpine

The total synthesis of (+)-pilocarpine (as its nitrate salt) has been achieved in nine steps and 30% overall yield starting from racemic 2-(2′,2′-dimethoxyethyl)propane-1,3-diol, which was desymmetrised via an enzymatic protocol. A high yielding synthesis of a key α-ethylidene lactone precursor has been developed, which involves the palladium-catalysed decarboxylation/carbonylation of a 1,3-dioxan-2-one for formation of the γ-butyrolactone ring. Subsequent hydrogenation of the α-ethylidene lactone introduces the C(3)-stereochemistry to give a 72:28 mixture of (+)-pilocarpine and (+)-isopilocarpine, which are readily separable via recrystallisation of the (+)-pilocarpine nitrate salt.     

A chemoenzymatic total synthesis of the Amaryllidaceae alkaloid narseronine

A 15-step and fully stereocontrolled total synthesis of the title alkaloid 1 has been accomplished using the enantiomerically pure and enzymatically-derived cis-1,2-dihydrocatechol 2 as starting material. The final and pivotal step involved the intramolecular hetero-Michael addition of secondary amine 16 to a tethered enone moiety followed by trapping of the resulting enolate through its reaction with an adjacent ester residue.     

A chemoenzymatic total synthesis of the hirsutene-type sesquiterpene (+)-connatusin B from toluene

The first total synthesis of the hirsutene-type sesquiterpenoid natural product (+)-connatusin B (2) is reported. The cis-1,2-dihydrocatechol 3, which is obtained in enantiomerically pure form via the enzymatic dihydroxylation of toluene, served as the starting material. Diels-Alder cycloaddition and oxa-di-π-methane rearrangement reactions represent key chemical steps in the reaction sequence leading to the cyclopropane ring-fused linear triquinane 14. Reductive cleavage of the three-membered ring within this framework and various functional group interconversions then provide the title compound 2.     

A chemoenzymatic approach enables the site‐specific conjugation of recombinant proteins

Many biotechniques including protein microarray, drug screening, biosensors rely on the immobilization of recombinant proteins on the solid supports. It is well known that random orientation of the immobilized proteins could impair their biologic functions. Thus, it is very important to develop new site‐specific immobilization approach. In this study, we presented a chemoenzymatic approach for site‐specific conjugation of recombinant proteins onto solid support. In this strategy, the affinity tag on recombinant protein was enzymatically cleaved to expose the N‐terminal serine, which was oxidized to carry an aldehyde group and was then covalently coupled to hydrazide resin through hydrazone ligation. As this approach takes advantage of the most frequently used TEV protease, it requires no further sequence design on recombinant protein. This method was validated by site specific coupling of a synthetic peptide and a recombinant protein onto solid supports. It was found that the site specific immobilized SH2 domain is functional and could be used to enrich tyrosine phosphorylated peptides.     

A one-pot chemoenzymatic synthesis of (2S, 4R)-4-methylproline enables the first total synthesis of antiviral lipopeptide cavinafungin B

We report an efficient ten-step (longest linear sequence) synthesis of antiviral natural product cavinafungin B in 37% overall yield. By leveraging a one-pot chemoenzymatic synthesis of (2S,4R)-4-methylproline and oxazolidine-tethered (AT (Boc)G-Rink resin) SPPS methodology, the assembly of our molecular target could be conducted in an efficient manner. This general strategy could prove amenable to the construction of other natural and unnatural linear lipopeptides. The value of incorporating biocatalytic steps in complex molecule synthesis is highlighted by this work.     

Enantioselective synthesis of natural (−)-tochuinyl acetate, (−)-dihydrotochuinyl acetate and (+)-β-cuparenone using both enantiomers of the same building block

The first enantioselective synthesis of tochuinyl acetate and dihydrotochuinyl acetate, two natural marine products isolated from Tochuina tetraquetra and Gersemia rubiformis, has been achieved starting from an enantiopure building block. The key feature of the present synthesis is complete control of two vicinal quaternary stereogenic centers present in the natural products and elucidation of their absolute stereochemistry, which was previously unknown. Furthermore, starting from the enantiomer of the same building block, the applied methodology provided a new approach towards natural (R)-(+)-β-cuparenone.     

Efficient chemoenzymatic synthesis of (2S,3R)-3-hydroxy-3-methylproline,a key fragment in polyoxypeptin A and FR225659

We report an efficient synthesis of protected (2S,3R)-3-hydroxy-3-methylproline that proceeds in three steps with complete stereoselectivity. This route represents a significant improvement over previous approaches to this noncanonical amino acid. Key to this success is the development of a one-pot chemoenzymatic procedure for the preparation of (2S,3S)-3-methylproline from l-isoleucine. This work lays the foundation for future chemoenzymatic syntheses of polyoxypeptin A and FR225659.     

A chemoenzymatic approach to glycopeptide antibiotics

Many biologically active natural products are constrained by macrocyclization and modified with carbohydrates. These two types of modifications are essential for their biological activities. Here we report a chemoenzymatic approach to make carbohydrate-modified cyclic peptide antibiotics. Using a thioesterase domain from the decapeptide tyrocidine synthetase, 13 head-to-tail cyclized tyrocidine derivatives were obtained with one to three propargylglycines incorporated at positions 3-8. These cyclic peptides were then conjugated to 21 azido sugars via copper(I)-catalyzed cycloaddition. Antibacterial and hemolytic assays showed that the two best glycopeptides, Tyc4PG-14 and Tyc4PG-15, have a 6-fold better therapeutic index than the natural tyrocidine. We believe this method will also be useful for modifying other natural products to search for new therapeutics.     

Designing for sustainability with biocatalytic and chemoenzymatic cascade processes

Cascade reactions have been widely recognized to cut costs, decrease solvent usage, and reduce cycle times in chemical processes. Recently, biocatalytic cascades have altered how we design synthetic routes to complex molecules to achieve sustainable commercial processes for pharmaceutical, agricultural, and fine chemical industries. With advancements in protein engineering and an increase in the number of enzyme classes available to chemists, industrial and academic groups alike have endeavored to expand the scope of biocatalysis from single reactions to multi-enzyme cascades to rapidly build complex molecular structures. Recent reports have drawn inspiration from biosynthetic pathways and have applied engineered enzymes to in vitro enzymatic cascades. Furthermore, combining transition-metal catalysis and enzymes in one-pot chemoenzymatic cascades likewise serves to broaden the scope of biocatalysis, enabling traditional chemical reactions to be performed under mild aqueous conditions. In this article, we review recent biocatalytic and chemoenzymatic cascades from 2019 to 2021.     

A chemoenzymatic synthesis of the linear triquinane (−)-hirsutene and identification of possible precursors to the naturally occurring (+)-enantiomer

An enantiomerically pure cis-1,2-dihydrocatechol, which is readily obtained via a toluene dioxygenase-mediated dihydroxylation of toluene in a whole-cell biotransformation process, has been converted over 17 steps into the linear triquinane (−)-hirsutene. Since the enantiomer of the starting material is also available this work constitutes a formal total synthesis of the naturally occurring (+)-form of hirsutene. Furthermore, minor modifications of the route used here offer the possibility of accessing (+)-hirsutene from the original starting material.     

A chemoenzymatic total synthesis of (+)-clividine

The title compound, ent-1, the non-natural enantiomeric form of the lycorenine-type alkaloid (-)-clividine (1), has been prepared using the enantiomerically pure (ee >99.8%) cis-1,2-dihydrocatechol 3 as starting material. A key feature associated with the closing stages of the synthesis involved the diastereoselective addition of a nitrogen-centered radical onto a pendant cyclohexene to establish the cis-fused D-ring and the required stereochemistry at C11b in the final product ent-1.     

A facial chemoenzymatic method for the preparation of chiral 1,2-dihydroxy-3,3,3,-trifluoropropanephosphonates

A convenient and effective method for the preparation of chiral trifluoromethylated 1,2-dihydroxypropanephosphonates based on a chemoenzymatic approach was described. Ethyl trifluoromethylacetate was reacted with anion of methylphosphonate to give 2-oxo-3,3,3-trifluoropropanephosphonate and its hydrates, 2,2-dihydroxy-3,3,3-trifluoropropanephosphonates, which are reduced with sodium boronhydride affording 2-hydroxy-3,3,3-trifluoropropanephosphonates. The product thus obtained was then transferred to corresponding 1,2-vinyl-3,3,3-trifluoropropanephosphonate and followed by 1,2-dihydroxylation via potassium permanganate treatment. Enzymatic kinetic resolution of the resultant racemate by CALB or IM provided optically active 1,2-dihydroxy-3,3,3-trifluoropropanephosphonate with satisfactory chemical and enantiomeric yield.     

First synthesis of (+)-myxothiazol A

First convergent synthesis of (+)-myxothiazol A (1) was achieved based on modified (one-pot) Julia olefination between (3,5R)-dimethoxy-(4R)-methyl 6-oxo-(2E)-hexenamide (2), corresponding to left-side of the final molecule, and E-4-2′-(1S,6-dimethylheptadiene)-(2,4′-bis-thiazole)-4-methybenzothiazole sulfone (4) corresponding to right-side.     

A concise synthesis of (+)-goniofufurone, (+)-7-epi-goniofufurone, (+)-crassalactones B and C

The concise and efficient synthesis of (+)-goniofufurone, (+)-7-epi-goniofufurone, (+)-crassalactones B and C were achieved in 6 to 7 steps from the known d-glucono-δ-lactone derivative 9. An acid-mediated cascade cyclization was employed to construct the furanofurone bicyclic framework in one-pot.     

Enantioselective, chemoenzymatic synthesis, and absolute configuration of the antioxidant (−)-gloeosporiol

The natural antioxidant (−)-gloeosporiol, isolated as a peracetylated derivative from a culture of the fungus Colletotrichum gloeosporioides, has been enantioselectively prepared from 3,4-dihydroxybenzaldehyde by means of a chemoenzymatic synthesis. The key intermediate was obtained by resolution with a lipase from Pseudomonas cepacia. Its stereochemistry, initially assigned as R, according to the Kazlaukas empirical rule for secondary alcohols, was independently confirmed by NMR and chirooptic methods. This, in turn, allowed the assignment of compound (−)-1 as (−)-(2S,3R,4R)-2-(3′,4′dihydroxyphenyl)tetrahydrofuran-3,4-diol.     

Chemoenzymatic total synthesis of cryptocaryalactone natural products

A new chemoenzymatic route for the preparation of cryptocaryalactones natural products using a kinetic resolution process as the key step is described. Novozyme-435 catalyzed hydrolysis of the prochiral (±)-monoester 7 afforded the precursors of cryptocaryalactones with high enantiomeric excess and excellent yields. The compounds (4S,6S)-7 and (4R,6R)-7 were converted to (+)-(6R,2′S)-cryptocaryalactone (1) and (?)-(6S,2′R)-cryptocaryalactone (2), respectively by employing Wittig-olefination, lactonization and acylation reactions.     

Synthetic studies toward (+)-cortistatin A

We describe herein the synthesis of a late-stage intermediate en route to cortistatin A. Key transformations included a Snieckus-like cascade sequence culminating in a 6π-electrocyclization, an alkylative dearomatization, and the stereoselective functionalization of the cortistatin A-ring. While the total synthesis we sought was not accomplished, the work sets the stage for several approaches to the preparation of novel analogs via diverted total synthesis.     

The first chemoenzymatic total synthesis of the phytotoxic nonenolide putaminoxin and its (5S,6E,9S)-diastereomer

The limitations of an alcohol dehydrogenase regarding the oxidative kinetic resolution of homoallylic alcohol containing alkyl chains were investigated, leading to a valuable building block for the total synthesis of phytotoxic nonenolide putaminoxin. The enzymatic approach towards the enantioenriched homoallylic alcohol was compared to classical, nonenzymatic approaches using asymmetric reagent controlled allyl additions and the obtained building block was used for the total synthesis of putaminoxin and its (5S,6E,9S)-diastereomer. After the spectroscopic analysis of the synthesized compounds, discrepancies were observed to already published data of isolated and synthesized putaminoxin. Therefore, a systematic comparison of NMR data was carried out. The result underlines the necessity of total synthesis for the absolute assignment of configuration.     

Concise synthesis of (+)-serinolamide A

Serinolamide A, isolated from a species of marine cyanobacteria, exhibits a moderate agonist effect and selectivity for the CB₁ cannabinoid receptor, which is unusual for marine natural products. Herein, we reported a highly efficient enantiospecific first total synthesis of (+)-serinolamide A from l-serine in nine steps with 30% overall yield. The synthesis method provides a facile, practicable, and economical approach for the preparation of other similar endocanabinoid lipids.     

Synthesis of (+)-boronolide and (+)-deacetylboronolide using Pd-catalyzed carbonylation and lactonization

(+)-Boronolide and (+)-deacetylboronolide were synthesized using Pd-catalyzed CO insertion and lactonization as the key step. As to the ¹³C NMR data of (+)-deacetylboronolide, the assignment at C-6 position should be revised.