Sugars containing α,β-unsaturated carbonyl systems: synthesis and their usefulness as scaffolds in carbohydrate chemistry

Synthesis of sugar enones and their use as powerful synthetic precursors of thiodisaccharides

Monosaccharide derivatives having a double bond conjugated to a carbonyl (sugar enones or enuloses) are relevant synthetic tools. They are also suitable starting materials, or versatile intermediates, for the synthesis of a wide variety of natural or synthetic compounds with a broad spectrum of biological and pharmacological activities. The preparation of enones is mainly focused on the search for more efficient and diastereoselective synthetic methodologies. The usefulness of enuloses relies on the diverse reaction possibilities offered by alkene and carbonyl double bonds, which are prone to undergo varied reactions such as halogenation, nitration, epoxidation, reduction, addition, etc. The addition of thiol groups that led to sulfur glycomimetics, such as thiooligosaccharides, is particularly relevant. Therefore, the synthesis of enuloses and the Michael addition of sulfur nucleophiles to give thiosugars or thiodisaccharides are discussed here. Chemical modifications of the conjugate addition products to afford biologically active compounds are also reported.

Rh(III)-catalyzed C-H annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins

The direct synthesis of isocoumarin skeletons has been realized through the Rh(III)-catalyzed [3 + 3] annulation of sulfoxonium ylides with iodonium carbenes. The synthetic protocol was constructed efficiently with broad functional group tolerance and mild reaction conditions. This reaction can be formally viewed as the result of C-H activation, carbene insertion and nucleophilic addition processes. Furthermore, the further conversions of the product and gram-scale reactions were also demonstrate to support the effectiveness of the synthesis protocol.

A Unified Strategy to Access 2- and 4-Deoxygenated Sugars Enabled by Manganese-Promoted 1,2-Radical Migration

The selective manipulation of carbohydrate scaffolds is challenging due to the presence of multiple, nearly chemically indistinguishable O-H and C-H bonds. As a result, protecting-group-based synthetic strategies are typically necessary for carbohydrate modification. Here we report a concise semisynthetic strategy to access diverse 2- and 4-deoxygenated carbohydrates without relying on the exhaustive use of protecting groups to achieve site-selective reaction outcomes. Our approach leverages a Mn²⁺-promoted redox isomerization step, which proceeds via sugar radical intermediates accessed by neutral hydrogen atom abstraction under visible light-mediated photoredox conditions. The resulting deoxyketopyranosides feature chemically distinguishable functional groups and are readily transformed into diverse carbohydrate structures. To showcase the versatility of this method, we report expedient syntheses of the rare sugars l-ristosamine, l-olivose, l-mycarose, and l-digitoxose from commercial l-rhamnose. The findings presented here validate the potential for radical intermediates to facilitate the selective transformation of carbohydrates and showcase the step and efficiency advantages attendant to synthetic strategies that minimize a reliance upon protecting groups.

Chemical and biological evaluation of unusual sugars, α-aculosides, as novel Michael acceptors

The unusual sugars, α-aculosides, which appear in certain antibiotics and have an α,β-unsaturated ketone structure, were found to be novel and selective Michael acceptors for the thiol function of cysteine residues. A coumarin derivative possessing α-aculoside as a Michael acceptor effectively and irreversibly operated as a fluorescent probe in cells. Furthermore, α-aculosides exhibited cytotoxic activity against several cancer cell lines.

Nano ZrO2: an efficient, recyclable, and inexpensive catalyst for diastereoselective three-component Mannich reactions

A facile procedure is developed for the three-component Mannich reactions of several heterocyclic, homocyclic, and acyclic ketones by using catalytic quantities of nano ZrO2. As a result, the starting ketones undergo rapid reactions with a variety of aromatic aldehydes and aniline derivatives at room temperature to produce stereoselectively high yields of the corresponding anti β-amino ketones. Interestingly, the catalyst could be recycled for several runs in a row without significant loss of its activity. The structure of the products was assigned based on their spectroscopic data and the anti stereoselectivity was confirmed by X-ray crystallography.

Efficient Synthesis of Dispiropyrrolidines Linked to Sugars

An expedient method for the synthesis of glyco-dispiropyrrolidines is reported through 1,3-dipolar cycloaddition reaction (1,3 DC reaction). The novel glycosyl dipolarophiles derived from D-glucose underwent neat [3+2] cycloaddition reaction with the azomethine ylides generated from 1,2-diketones and sarcosine to give the corresponding glycosidic heterocycles in good yields.

Synthesis and in vitro antitumor activity of new butenolide-containing dithiocarbamates

Three series of butenolide-containing dithiocarbamates were designed and synthesized. Their anti-tumor activity in vitro was evaluated. Among them compound I-14 exhibited broad spectrum anti-cancer activity against five human cancer cell lines with IC(50) <30 μM. Structure-activity relationship analysis showed that the introduction of dithiocarbamate side chains on the C-3 position of butenolide was crucial for anti-tumor activity.

Synthesis and antitumor evaluation of methyl spongoate analogs

A series of novel methyl spongoate (1) analogs has been synthesized and evaluated for their in vitro cytotoxic properties. It was found that the nature of the C-20 side chain had significant effects on their bioactivities and some analogs showed higher cytotoxicity than 1 against A549, HCT-116, HepG2, SW-1990, MCF-7 and NCI-H460 tumor cell lines. The pharmacological results confirmed that the α,β-unsaturated carbonyl moiety, a Michael acceptor in ring A, plays a pivotal role in the cytotoxic effect of these derivatives. The compiled pharmacological data may be useful for the design of novel analogous anticancer drugs.

Furanose C-C-linked γ-lactones: a combined ESI FTICR MS and semi-empirical calculations study

Sugars that incorporate the unsaturated carbonyl motif have become important synthetic targets not only as a result of their potential biological properties but also as precursors in the synthesis of many bioactive products. Moreover, little is known about the influence of the γ-lactone moiety in the fragmentation pattern of furanose rings. Therefore, two α,β-unsaturated γ-lactones (butenolides) and two β-hydroxy γ-lactones, C-C linked to a furanose ring were studied using electrospray ionization FTICR mass spectrometry. The behaviour of the protonated and sodiated forms of the compounds under study has been compared considering their structural features. Fragmentation mechanisms were established and ion structures were proposed taking into account the MS(2) and MS(3) experiments, accurate mass measurements and semi-empirical calculations. These inexpensive methods proved to be a valuable resource for proposing protonation sites and for the establishment of fragmentation pathways.

Electrospray ionization mass spectrometric analysis of newly synthesized alpha,beta-unsaturated gamma-lactones fused to sugars

Knowledge of the fragmentation mechanisms of lactones and their behaviour under electrospray ionization (ESI) conditions can be extended to larger and more complex natural products that contain an alpha,beta-unsaturated gamma-lactone moiety in their structure. Moreover, little is known about the gas-phase behaviour of alpha,beta-unsaturated gamma-lactones linked or fused to sugars. Therefore, five alpha,beta-unsaturated gamma-lactones (butenolides) fused to a pyranose ring, recently synthesized compounds with potential relevance regarding their biological properties, were investigated using ESI-MS and ESI-MS/MS in both positive and negative ion modes. Their fragmentation mechanisms and product ion structures were compared. It was observed that two isomers could be unambiguously distinguished in the negative ion mode by the fragmentation pathways of their deprotonated molecules as well as in the positive ion mode by the fragmentation pathways of either the protonated or the sodiated molecule. Fragmentation mechanisms are proposed taking into account the MS/MS data and semi-empirical calculations using the PM6 Hamiltonean. The semi-empirical calculations were also very useful in determining the most probable protonation and cationization sites.