Synthesis of C-Aryl Furanosides by the “Reverse Polarity” Strategy

Synthetic access to thiolane-based therapeutics and biological activity studies

Secondary metabolites isolated from bioactive extracts of natural sources iteratively pioneer the research in drug discovery. Modern medicine is often inspired by bioactive natural products or the bio-functional motifs embedded in them. One of such consequential bio-functional motifs is the thiolane unit. Thiolane-based bioactive organic compounds have manifested a plethora of astonishing biological activities such as anti-viral, anti-cancer, anti-platelet, α-glucosidase inhibition, anti-HIV, immunosuppressive and anti-microbial activities which renders them excellent candidates in drug discovery. Hence, to scale up the accessibility of thiolane-based therapeutics its chemical syntheses is essential and in addition; a sneak peek in its biosynthesis would give a perspective for developing biomimetic syntheses. This review highlights the development of important thiolane-based therapeutics such as (i) Nuphar sesquiterpene thioalkaloids (ii) Thiosugar sulphonium salts from Salacia sp. (iii) Albomycins (iv) Thiolane-based therapeutics from Allium sp. (v) 4'-thionucleosides summarizing various synthetic strategies, biosynthesis and biological activity studies, covering literature till 2021. We anticipate that this review will inspire chemists and biochemists to take up the challenges encountered in the synthesis and development of thiolane-based therapeutics.

The evolution of comprehensive strategies for furanoid glycal synthesis and their applications

Cyclic enol ether frameworks, especially stereochemically pure furanoid and pyranoid glycals are well known highly functionalized chiral building blocks.

Regioselective synthesis of naphthoquinone/naphthoquinol-carbohydrate hybrids by [4 + 2] anionic annulations and studies on their cytotoxicity

An efficient and regioselective synthetic route to naphthoquinone/naphthoquinol-carbohydrate hybrids has been developed. It is based upon anionic annulation of 3-nucleofugalphthalides with an acrylate appended sugar moiety. In each of the annulations studied, the arene-carbohydrate hybrids were obtained in good to excellent yields. The in vitro cytotoxic activity of the synthetic naphthoquinone/naphthonol-carbohydrate hybrids were evaluated against the human cervical cancer cell line (HeLa), and a few of them were found to exhibit potent anticancer activity against the cell line.

Stereoselective C-glycosidation of D-fucose derivatives directed by the protective groups

Stereoselectivity in the C-glycosidation of lactones derived from D-fucose by following Kishi's method, which involves the addition of a nucleophile onto a carbohydrate-derived lactone and subsequent reduction of the lactol, was found to be reliant on the nature of the C2 and C3 protective groups. Lactones bearing TBDMS protecting groups selectively afford 1,3-trans products (α anomer), in which the stereoselective outcome is in apparent concordance with Woerpel's model. On the other hand, their benzylated congeners produce the 1,3-cis products (β anomer) as the major diastereoisomers. The latter results suggest an abnormal behavior during the stereoselective nucleophilic substitution at the anomeric position of the benzylated lactones.

Synthesis of conformationally North-locked pyrimidine nucleosides built on an oxabicyclo[3.1.0]hexane scaffold

Beginning with a known 3-oxabicyclo[3.1.0]hexane scaffold (I), the relocation of the fused cyclopropane ring bond and the shifting of the oxygen atom to an alternative location engendered a new 2-oxabicyclo[3.1.0]hexane template (II) that mimics more closely the tetrahydrofuran ring of conventional nucleosides. The synthesis of this new class of locked nucleosides involved a novel approach that required the isocyanate II (B = NCO) with a hydroxyl-protected scaffold as a pivotal intermediate that was obtained in 11 steps from a known dihydrofuran precursor. The completion of the nucleobases was successfully achieved by quenching the isocyanate with the lithium salts of the corresponding acrylic amides that led to the uracil and thymidine precursors in a single step. Ring closure of these intermediates led to the target, locked nucleosides. The anti-HIV activity of 29 (uridine analogue), 31 (thymidine analogue), and 34 (cytidine analogue) was explored in human osteosarcoma (HOS) cells or modified HOS cells (HOS-313) expressing the herpes simplex virus 1 thymidine kinase (HSV-1 TK). Only the cytidine analogue showed moderate activity in HOS-313 cells, which means that the compounds are not good substrates for the cellular kinases.

Pectenotoxin-2 synthetic studies. 1. Alkoxide precoordination to [Rh(NBD)(DIPHOS-4)]BF(4) allows directed hydrogenation of a 2,3-dihydrofuran-3-ol without competing furan production

[reaction: see text] The alkoxide-directed hydrogenation shown is reported as a key step in a concise synthesis of a fully functionalized precursor to the C29-C40 F/G sector of pectenotoxin-2.