Chiral Imidazolidin-4-one with catalytic amount of Dicationic ionic liquid act as a recoverable and reusable Organocatalyst for asymmetric Diels-Alder reaction

Imidazolidin-4-one is used as a recoverable organocatalyst for the asymmetric Diels-Alder reaction in the presence of catalytic amount of dicationic ionic liquid and trifluoroacetic acid as a co-catalyst. The Diels-Alder reaction between model substrate cyclopentadiene and crotonaldehyde gave the product in 95% conversion and 87% ee of the endo-product. The catalyst was shown better reusability when the 20 mol% of dicationic ionic liquid was used and catalyst was reused upto 5 cycles, conversion remains upto 3 recycles but ee of endo- 9 was slightly droped.     

Enantioselective total synthesis of altersolanol A and N

The development of the first enantioselective total synthesis of altersolanol N is reported. The decisive step of the synthesis is the enantioselective formation of the tetrahydroanthraquinone nucleus by a [4 + 2]-cycloaddition in high yield and with excellent diastereo- and enantioselectivity (>95:5 dr and 95:5 er). In addition, a demanding selective monoacetylation of the OH group at the C-2 position was achieved: an epoxide ring opening with the participation of a neighbouring acetyl group could be established. The route proved to be an efficient alternative to also access enantiomerically pure altersolanol A.     

Synthesis of conformationally constrained hydroxy-α-amino acids by intramolecular conjugate addition

Summary. An efficient and easily applicable method for the synthesis of a variety of hydroxy-α-amino acids analogues of serine and phenylalanine has been established. The method involves the stereoselective intramolecular conjugate addition of the benzamide group to cyclohexenone promoted by Lewis acid. Subsequent transformations of functional groups pro-vide the conformationally constrained 2-hydroxy- and 2,4-dihydroxy-6-phenylcyclohexane-α-amino acids. Received February 5, 1999, Accepted May 16, 1999     

Diels-Alder route to steroids and associated structures

The Diels-Alder reaction continues to dominate the developments in steroid synthesis. A review of literature on the Diels-Alder route to steroids is presented.     

Synthesis of FF8181-A

Both enantiomers of FF8181-A were synthesized through optical resolution from the known Diels-Alder reaction product in 15 steps. The absolute configuration of the natural product was determined to be 1S,5S,5aS,9aS,9bS.     

Harnessing the Bioorthogonal Inverse Electron Demand Diels-Alder Cycloaddition for Pretargeted PET Imaging

Due to their exquisite affinity and specificity, antibodies have become extremely promising vectors for the delivery of radioisotopes to cancer cells for PET imaging. However, the necessity of labeling antibodies with radionuclides with long physical half-lives often results in high background radiation dose rates to non-target tissues. In order to circumvent this issue, we have employed a pretargeted PET imaging strategy based on the inverse electron demand Diels-Alder cycloaddition reaction. The methodology decouples the antibody from the radioactivity and thus exploits the positive characteristics of antibodies, while eschewing their pharmacokinetic drawbacks. The system is composed of four steps: (1) the injection of a mAb-trans-cyclooctene (TCO) conjugate; (2) a localization time period during which the antibody accumulates in the tumor and clears from the blood; (3) the injection of the radiolabeled tetrazine; and (4) the in vivo click ligation of the components followed by the clearance of excess radioligand. In the example presented in the work at hand, a ⁶⁴Cu-NOTA-labeled tetrazine radioligand and a trans-cyclooctene-conjugated humanized antibody (huA33) were successfully used to delineate SW1222 colorectal cancer tumors with high tumor-to-background contrast. Further, the pretargeting methodology produces high quality images at only a fraction of the radiation dose to non-target tissue created by radioimmunoconjugates directly labeled with ⁶⁴Cu or ⁸⁹Zr. Ultimately, the modularity of this protocol is one of its greatest assets, as the trans-cyclooctene moiety can be appended to any non-internalizing antibody, and the tetrazine can be attached to a wide variety of radioisotopes.     

Three new sesquiterpene lactone dimers from Carpesium faberi

Three new 2,4-linked sesquiterpene lactone dimers (SLDs), faberidilactones F-H (1–3), have been isolated from Carpesium faberi. Unlike 1 and 2, 3 was a modified Diels-Alder adduct, characteristic by a 1′-OH and a Δ^5′(6′) double bond. Furthermore, the relative configuration of 1′-OH in 3 was assigned as β-configuration by comparison the experimental NOESY data with those of its two possible epimers. The exo/endo stereochemistry of 1–3 was determined by the spectrographic features of 2,4-linked SLDs that we discovered in our previous works. Compounds 1 and 2 showed potent cytotoxicity against human leukemia (CCRF-CEM) cells with IC₅₀ value of 5.62 and 3.74 μM, respectively.     

长穗桑中的Diels-Alder型加合物

从长穗桑的茎皮中首次分离到9个Diels—Alder型加合物,通过NMR、MS等波谱分析手段分别鉴定为mulberrofuran K（1）,mulberrofuran G（2）,guangsangon L（3）,kuwanon J（4）,kuwanonx（5）,guangsangonG（6）,guangsangon B（7）,guangsangon D（8）,kuwanon P（9）。化合物1—9进行了抗氧化活性筛选。结果表明,在10^-5M浓度下,化合物1,2,5—7,9对Fe^2＋-半胱氨酸诱导的肝微粒体脂质过氧化产生的丙二醛（malondialdehyde,MDA）有抑制作用（抑制率大于50％）。     

Guangsangons F-J, anti-oxidant and anti-inflammatory Diels-Alder type adducts, from Morus macroura Miq

Five Diels-Alder type adducts, named guangsangons F, G, H, I, and J, along with two known compounds, mulberrofuran J and kuwanon J, were isolated from Morus macroura Miq. Their structures were determined by means of spectroscopic analyses and chemical methods. These compounds were regarded biogenetically as Diels-Alder type adducts of dehydroprenylphenols and chalcone derivatives, and (1)H NMR variable temperature experiments suggested that they all existed as an equilibrium mixture of conformational isomers in solution. Among the isolated new compounds, guangsangons H, I, and J displayed potent antioxidant activities and moderate anti-inflammatory activities.     

Native transfer RNA catalyzes Diels-Alder reaction

In this paper we show that transfer ribonucleic acids (tRNAs) catalyze the Diels-Alder cycloaddition reaction. A new DNA oxidative damage product, 6-furfuryladenine (kinetin) or its riboside (diene), was transformed with dimethyl acetylenedicarboxylate or maleic anhydride (dienophile). The reaction proceeds in the presence of tRNA at high pressure but not at ambient condition. If so tRNA in prebiotic conditions (RNA world) had at least two functions: catalytic and a carrier of genetic information. It means that tRNA at high pressure shows catalytic properties and is a true Diels-Alderase.