Novel and Efficient Syntheses of (−)-Methyl 4-epi-Shikimate and 4,5-Epoxy-Quinic and -Shikimic Acid Derivatives as Key Precursors to Prepare New Analogues

Chemo-enzymatic total synthesis of the spirosorbicillinols

The natural product class of the sorbicillinoids is composed of structurally diverse molecules with many strong, biomedically relevant biological activities. Owing to their complex structures, the synthesis of sorbicillinoids is a challenging task. Here we show the first total synthesis of the fungal sorbicillinoids spirosorbicillinols A-C. The convergent route comprises the chemo-enzymatic transformation of sorbicillin to the highly reactive sorbicillinol and the assembly of scytolide and isomers starting from shikimic and quinic acid analogs. The key step in the total synthesis is the fusion of both building blocks in a Diels-Alder cycloaddition leading to the straightforward formation of the characteristic sorbicillinoid bicyclo[2.2.2]octane backbone. This work provides unifying access to all natural spirosorbicillinols and unnatural diastereomers.

Halogen-atom and group transfer reactivity enabled by hydrogen tunneling

The generation of carbon radicals by halogen-atom and group transfer reactions is generally achieved using tin and silicon reagents that maximize the interplay of enthalpic (thermodynamic) and polar (kinetic) effects. In this work, we demonstrate a distinct reactivity mode enabled by quantum mechanical tunneling that uses the cyclohexadiene derivative γ-terpinene as the abstractor under mild photochemical conditions. This protocol activates alkyl and aryl halides as well as several alcohol and thiol derivatives. Experimental and computational studies unveiled a noncanonical pathway whereby a cyclohexadienyl radical undergoes concerted aromatization and halogen-atom or group abstraction through the reactivity of an effective H atom. This activation mechanism is seemingly thermodynamically and kinetically unfavorable but is rendered feasible through quantum tunneling.

Practical synthesis of ECH and epoxyquinols A and B from (-)-shikimic acid

An efficient synthesis of ECH, epoxyquinols A and B, and two bioactive analogs EqM and RKTS-33 has been completed starting from (-)-shikimic acid. Rapid establishment of the desired epoxyquinol core is facilitated through a key allylic oxidation with high stereoselectivity, which is achieved by fine tuning the cyclohexene substrate structure and reaction conditions.

Current Advances in Naturally Occurring Caffeoylquinic Acids: Structure, Bioactivity, and Synthesis

Caffeoylquinic acids (CQAs) are a broad class of secondary metabolites that have been found in edible and medicinal plants from various families. It has been 100 years since the discovery of chlorogenic acid in 1920. In recent years, a number of naturally derived CQAs have been isolated and structurally elucidated. Accumulated evidence demonstrate that CQAs have a wide range of biological activities, such as antioxidation, antibacterial, antiparasitic, neuroprotective, anti-inflammatory, anticancer, antiviral, and antidiabetic effects. Up to date, some meaningful progresses on the biosynthesis and total synthesis of CQAs have also been made. Therefore, it is necessary to comprehensively summarize the structure, biological activity, biosynthesis, and chemical synthesis of CQAs. This review provides extensive coverage of naturally occurring CQAs discovered from 1990 until 2020. Modern isolation techniques, chemical data (including structure, biosynthesis, and total synthesis), and bioactivity are summarized. This would be helpful for further research of CQAs as potential pharmaceutical agents.

Gram-scale carbasugar synthesis via intramolecular seleno-Michael/aldol reaction

Carbasugars represent an important category of natural products possessing a broad spectrum of biological activities. Lots of effort has been done to develop gram scale synthesis. We are presenting a new approach to gram scale synthesis of the carbasugar skeleton via intramolecular seleno-Michael/aldol reaction. The proposed strategy gave gram amounts of 6-hydroxy shikimic ester in a tandem process in 36% overall yield starting from d-lyxose. We have attempted to demonstrate the synthetic utility of 6-hydroxyshikimic acid derivatives by covering the important synthetic modifications and related applications, namely synthesis of protected (−)-gabosine E, (−)-MK7606, (−)-valienamine and finally unprotected methyl (−)-shikimate.

A new approach to gram scale synthesis of carbasugar derivatives via intramolecular seleno-Michael/aldol reaction.

Production and Synthetic Modifications of Shikimic Acid

Shikimic acid is a natural product of industrial importance utilized as a precursor of the antiviral Tamiflu. It is nowadays produced in multihundred ton amounts from the extraction of star anise ( Illicium verum) or by fermentation processes. Apart from the production of Tamiflu, shikimic acid has gathered particular notoriety as its useful carbon backbone and inherent chirality provide extensive use as a versatile chiral precursor in organic synthesis. This review provides an overview of the main synthetic and microbial methods for production of shikimic acid and highlights selected methods for isolation from available plant sources. Furthermore, we have attempted to demonstrate the synthetic utility of shikimic acid by covering the most important synthetic modifications and related applications, namely, synthesis of Tamiflu and derivatives, synthetic manipulations of the main functional groups, and its use as biorenewable material and in total synthesis. Given its rich chemistry and availability, shikimic acid is undoubtedly a promising platform molecule for further exploration. Therefore, in the end, we outline some challenges and promising future directions.

Application of Heterogeneous Catalysts in the First Steps of the Oseltamivir Synthesis

The first steps of oseltamivir synthesis from quinic acid involve acetalization and ester formation. These reactions are catalyzed by either acids or bases, which may be accomplished by heterogeneous catalysts. Sulfonic solids are efficient acid catalysts for acetalization and esterification reactions. Supported tetraalkylammonium hydroxide or 1,5,7-triazabicyclo[4.4.0]dec-5-ene are also efficient base catalysts for lactone alcoholysis and in this work, these catalysts have been applied in two alternative synthetic routes that lead to oseltamivir. The classical route consists of an acetalization, followed by a lactonization, and then a lactone alcoholysis. This achieves a 66% isolated yield. The alternative route consists of esterification followed by acetalization and is only efficient when an acetone acetal is used.

The hydrophobic side chain of oseltamivir influences type A subtype selectivity of neuraminidase inhibitors

Neuraminidase, which plays a critical role in the influenza virus life cycle, is a target for new therapeutic agents. The study of structure-activity relationships revealed that the C-5 position amino group of oseltamivir was pointed to 150-cavity of the neuraminidase in group 1. This cavity is important for selectivity of inhibitors against N1 versus N2 NA. A serial of influenza neuraminidase inhibitors with the oseltamivir scaffold containing lipophilic side chains at the C-5 position have been synthesized and evaluated for their influenza neuraminidase inhibitory activity and selectivity. The results indicated that compound 13o (H5N1 IC₅₀  = 0.1 ± 0.04 μm, H3N2 IC₅₀  = 0.26 ± 0.18 μm) showed better inhibitory activity and selectivity against the group 1 neuraminidase. This study may provide a clue to design of better group 1 neuraminidase inhibitors.

Synthesis, Structure, and Tandem Mass Spectrometric Characterization of the Diastereomers of Quinic Acid

(-)-Quinic acid possess eight possible stereoisomers, which occur both naturally and as products of thermal food processing. In this contribution, we have selectively synthesized four isomers, namely, epi-quinic acid, muco-quinic acid, cis-quinic acid, and scyllo-quinic acid, to develop a tandem LC-MS method identifying all stereoisomeric quinic acids. Four derivatives have been unambiguously characterized by single-crystal X-ray crystallography. The missing diastereomers of quinic acid were obtained by nonselective isomerization of (-)-quinic acid using acetic acid/concentrated H2SO4 allowing chromatographic separation and assignment of all diastereomers of quinic acid. We report for the first time that a full set of stereoisomers are reliably distinguishable on the basis of their tandem mass spectrometric fragment spectra as well as their elution order. A rationale for characteristic fragmentation mechanisms is proposed. In this study, we also observed that muco-quinic acid, scyllo-quinic acid, and epi-quinic acid are present in hydrolyzed Guatemalan roasted coffee sample as possible products of roasting.

Asymmetric Total Syntheses of ent-Ascospiroketals A and B

A new hypothetic biosynthesis of the tricyclic spiroketal core of ascospiroketals A and B is proposed, which guided the development of a novel synthetic strategy for the asymmetric total synthesis of ent-ascospiroketals A and B. The synthesis features an efficient ring contraction rearrangement of the 10-membered lactone to the tricyclic spiroketal cis-fused γ-lactone core, which served as the common intermediate for the synthesis of both ent-ascospiroketals A and B through the Stille coupling reaction at the final step. In addition, seven diastereomers were prepared to conclusively confirm the structure of ent-ascospiroketal B.

Generation of aroE overexpression mutant of Bacillus megaterium for the production of shikimic acid

Background

Shikimic acid, the sole chemical building block for the antiviral drug oseltamivir (Tamiflu®), is one of the potent pharmaceutical intermediates with three chiral centers. Here we report a metabolically engineered recombinant Bacillus megaterium strain with aroE (shikimate dehydrogenase) overexpression for the production of shikimic acid.

Results

In a 7 L bioreactor, 4.2 g/L shikimic acid was obtained using the recombinant strain over 0.53 g/L with the wild type. The enhancement of total shikimate dehydrogenase activity was 2.13-fold higher than the wild type. Maximum yield of shikimic acid (12.54 g/L) was obtained with fructose as carbon source. It was isolated from the fermentation broth using amberlite IRA-400 resin and 89 % purity of the product was achieved.

Conclusion

This will add up a new organism in the armory for the fermentation based production which is better over plant based extraction and chemical synthesis of shikimic acid.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0251-3) contains supplementary material, which is available to authorized users.

Facile synthesis of the cyclohexane fragment of enacloxins, a series of antibiotics isolated from Frateuria sp. W-315

An efficient and good yield synthesis of the cyclohexane moiety of enacyloxins, a series of antibiotics isolated from Frateuria sp. W-315, was achieved from d-quinic acid using a successive Barton-McCombie deoxygenation.

Synthesis of the anti-influenza agent (-)-oseltamivir free base and (-)-methyl 3-epi-shikimate

A new enantioselective synthesis of the anti-influenza agent (-)-oseltamivir free base (7.1% overall yield; 98% ee) and (-)-methyl 3-epi-shikimate (16% overall yield; 98% ee) has been described from readily available raw materials. Sharpless asymmetric epoxidation and diastereoselective Barbier allylation of an aldehyde are the key reactions employed in the incorporation of chirality, while the cyclohexene carboxylic ester core was constructed through a ring closing metathesis reaction.

Production of shikimic acid

Shikimic acid is a key intermediate for the synthesis of the antiviral drug oseltamivir (Tamiflu®). Shikimic acid can be produced via chemical synthesis, microbial fermentation and extraction from certain plants. An alternative production route is via biotransformation of the more readily available quinic acid. Much of the current supply of shikimic acid is sourced from the seeds of Chinese star anise (Illicium verum). Supply from star anise seeds has experienced difficulties and is susceptible to vagaries of weather. Star anise tree takes around six-years from planting to bear fruit, but remains productive for long. Extraction and purification from seeds are expensive. Production via fermentation is increasing. Other production methods are too expensive, or insufficiently developed. In the future, production in recombinant microorganisms via fermentation may become established as the preferred route. Methods for producing shikimic acid are reviewed.

Rapid assembly of potent type II dehydroquinase inhibitorsvia “Click” chemistry

The rapid synthesis of a library of potent type II dehydroquinase inhibitors is described. Inhibitors were prepared via a key quinate-derived ene-yne intermediate using Cu(i)-catalysed azide-alkyne cycloaddition (CuAAC) chemistry with a variety of aryl- and heteroaryl-azides.

Synthesis, conformational analysis, and biological evaluation of 19-nor-vitamin D3 analogues with A-ring modifications

We have synthesized several isomers of 19-nor-vitamin D analogues possessing a hydroxy group at C-2 as well as novel derivatives bearing an epoxy substituent at the A-ring. All vitamins were prepared in convergent syntheses utilizing the modified Julia olefination. 1alpha,2alpha,25-Trihydroxy-19-nor-vitamin D(3) (3) and 2beta,3beta-epoxy-1alpha,25-dihydroxy-3-deoxy-19-nor-vitamin D(3) (10), which showed the highest affinity to the vitamin D receptor, displayed the highest potency among the tested compounds to inhibit the proliferation of MCF-7 breast cancer cells.

Facile and efficient synthesis of naturally occurring carbasugars (+)-pericosines A and C

An efficient synthesis of antitumor marine natural product (+)-pericosine A was achieved from (-)-quinic acid in 11.7% overall yield, which is 20 times better than our previously reported synthesis. The crucial steps of this synthesis include the regio- and stereoselective bromohydrination of an unstable diene and the ring opening of an epoxide. This synthetic route was applicable to a synthesis of (+)-pericosine C and also to a synthesis of (-)-pericosine C.

Synthesis of the Naturally Occurring (-)-1,3,5-Tri-O-Caffeoylquinic Acid

Ribonuclease H (RNase H) is an essential component to the replication of human immunodeficiency virus (HIV), and only a few inhibitors of this enzyme are known. Millenia Hope Pharmaceuticals Inc. found that (-)-1,3,5-tri-O-caffeoylquinic acid is a potent RNase H inhibitor and antiviral agent. A facile route leading to this inhibitor from commercially available (-)-quinic acid is reported within.

First Total Synthesis of Antitumor Natural Product (+)- and (−)-Pericosine A: Determination of Absolute Stereo Structure†

The first total synthesis of (+)- and (-)-pericosine A has been achieved, enabling the revision and determination of the absolute configuration of this antitumor natural product as methyl (3S,4S,5S,6S)-6-chloro-3,4,5-trihydroxy-1-cyclohexene-1-carboxylate. Every step of this total synthesis proceeded well with excellent stereoselectivity. Structures of the intermediates in crucial steps were confirmed by detailed 2D NMR analysis.

Synthesis and biological evaluation of new 6-s-cis locked 1,2,25-trihydroxyprevitamin D3 analogues

An efficient synthesis of several diastereomers of 2-hydroxy substituted 1alpha,25-dihydroxyprevitamin D3 derivatives was accomplished utilizing a practical route to the A-ring synthon. The biological activity of the analogues was evaluated in vitro. All the synthesized derivatives demonstrated low affinity for the vitamin D receptor and vitamin D-binding protein compared with 1alpha,25-dihydroxyvitamin D3, the natural hormone. 1alpha,2beta,25-trihydroxy-19-nor-pre-D3 was the most potent of the analogues in inhibiting proliferation of MCF-7 cells but requires higher EC50 concentrations than 1alpha,25-dihydroxyvitamin D3.