scholarly journals A mutually stabilized host-guest pair

2019 ◽  
Vol 5 (11) ◽  
pp. eaax6707 ◽  
Author(s):  
Chi Zhang ◽  
Hongye Wang ◽  
Jie Zhong ◽  
Ye Lei ◽  
Renfeng Du ◽  
...  

By using click chemistry, a hexacationic cage was synthesized. The cage contains two triscationic π-electron–deficient trispyridiniumtriazine (TPZ3+) platforms that are bridged in a face-to-face manner by three ethylene-triazole-ethylene linkers. A diversity of π-electron–rich guests can be recognized within the pocket of the cage, driven by host-guest π-π interactions. The cage cavity acts as a protecting group, preventing an anthracene guest from undergoing Diels-Alder reaction. Under ultraviolet (UV) light, the pyridinium C─N bonds in TPZ3+ platforms are polarized and weakened, resulting in the occurrence of cage decomposition via β-elimination. Guest recognition could help to prevent this UV-stimulated cage decomposition by suppressing the excitation of the TPZ3+ units.

1997 ◽  
Vol 52 (7) ◽  
pp. 851-858 ◽  
Author(s):  
Gunther Seitz ◽  
Johanna Siegl

The anomeric imido esters 5 and 6, appropriate precursors for C-nucleoside synthesis, were prepared and utilized as heterodienophiles in a Diels-Alder reaction with inverse electron demand to yield the novel, protected 1.2.4-triazine C-nucleosides 8 and 9. They could be deprotected by treatment with 70% trifluoroacetic acid to furnish the free C-nucleosides 10 and 11. The triazine „aglycon“ of 8 contains an electron deficient diazadiene system, highly activated to react with various electron rich dienophiles such as enamines, enol ethers and several cyclic ketene acetals in an „inverse“ [4+2]-cycloaddition reaction. The Diels-Alder adducts spontaneously eliminate N2 and after follow-up reactions the O-TBDPS protected pyridine-C-nucleosides 13, 15, 17,19, 21 and 23 are formed. Removal of the protecting group by treatment with CF3CO2H /H2O leads to the corresponding 2’,3’-dideoxy-β-D-ribofuranosyl- pyridines.


Author(s):  
Douglass Taber

( + )-Superstolide A 3, isolated from the New Caledonian sponge Neosiphonia superstes, shows interesting cytotoxicity against malignant cell lines at ~ 4 ng/mL concentration. The key transformation in the synthesis of 3 described (J. Am. Chem. Soc. 2008, 130, 2722) by William R. Roush of Scripps Florida was the transannular Diels-Alder cyclization of 2, which established, in one step with high diastereocontrol, both the cis decalin and the macrolactone of 3. The octaene 1 was assembled from four stereodefined fragments. The first, the linchpin 6, was prepared from the stannyl aldehyde 4. Homologation gave the enyne 5, which on hydroboration and oxidation gave 6. Earlier, Professor Roush had optimized the crotylation of the protected alaninal 7. In this case, the Brown reagent 8 delivered the desired Felkin product 9. Protection followed by ozonolysis gave the aldehyde 10. Crotylation with the Roush-developed tartrate 11 then gave the alkene 12, setting the stage for conversion to the iodide 13. Coupling of 13 with 6 completed the preparation of 14. The third component of (+)-superstolide A 3, the phosphonium salt 21, was assembled by Brown allylation of the aldehyde 15, to give 17. Protecting group interchange followed by ozonolysis delivered 18, which via Still-Gennari homologation was carried on to 21. Condensation with the fourth component, the aldehyde 22 , and esterification with 14 then gave 1. Under high dilution Suzuki conditions 1 was converted to 2. Storage in CDCl3 for five days, or brief warming, cyclized 2 to a single diastereomer of the transannular Diels-Alder product, that was carried on to (+)-superstolide A 3. While acyclic trienes comparable to 2 could be induced to cyclize, the transannular Diels-Alder reaction proceeded with much higher diastereocontrol.


Synthesis ◽  
2021 ◽  
Author(s):  
Adisak Thanetchaiyakup ◽  
Hassayaporn Rattanarat ◽  
Sudaporn Aree ◽  
Tanwawan Duangthongyou ◽  
Tanin Nanok ◽  
...  

Melotenine A, isolated from Melodinus tenuicaudatus, possesses significant anticancer activity against several human cancer cell lines. The synthesis of (±)-melotenine A was achieved without the use of any protecting groups in 11 steps with an overall yield of 7%. The key steps of our strategy were the Diels–Alder reaction to construct the tetracyclic framework and ring-closing metathesis to form the seven-membered ring of (±)-melotenine A.


2014 ◽  
Vol 38 (12) ◽  
pp. 5975-5982 ◽  
Author(s):  
Jens H. Aasheim ◽  
Heike Fliegl ◽  
Einar Uggerud ◽  
Tore Bonge-Hansen ◽  
Odile Eisenstein

The preferred stereoisomeric product of this catalytic Diels–Alder reaction is in part determined by noncovalent CH⋯π interactions.


2013 ◽  
Vol 85 (7) ◽  
pp. 1499-1513 ◽  
Author(s):  
Selvanathan Arumugam ◽  
Sara V. Orski ◽  
Ngalle Eric Mbua ◽  
Christopher McNitt ◽  
Geert-Jan Boons ◽  
...  

Three photo-click ligation strategies described in this account provide scientists with efficient and selective tools for derivatization of various molecules, polymers, and surfaces. Fast photochemical reactions that are utilized in these techniques permit spatiotemporal control of the process. The absence of activating reagents and catalysts, as well as compatibility with aqueous media, makes photo-click ligations suitable for biomedical applications. The first of these approaches relies on the photochemical decarbonylation of cyclopropenones to produce cyclooctynes. The latter undergo rapid catalyst-free strain-promoted azide–alkyne cycloaddition (SPAAC) to azide-tagged substrates. The second method is based on a very fast (>104 M–1 s–1) light-triggered hetero-Diels–Alder reaction and permits efficient derivatization of substrates bearing vinyl ether moiety. An even faster reaction between photochemically generated naphthoquinone methides (oNQMs) and thiols (~2 × 105 M–1 s–1) serves as a basis for a third method. This thiol photo-click chemistry allows for the selective derivatization of thiol-functionalized substrates or labeling of free cysteine residues in proteins. The thioether linkage produced by the reaction of oNQMs and a thiol is stable under ambient conditions, but can be cleaved by UV irradiation, regenerating free thiol. This feature permits the removal or replacement of immobilized compounds, as well as traceless substrate release.


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