One-step preparation of 1-substituted tetrahydroisoquinolines via the Pictet–Spengler reaction using zeolite catalysts

Isoquinoline alkaloids from Corydalis edulis Maxim. Exhibiting insulinotropic action

Eleven undescribed isoquinoline analogues, namely edulisines A-K, along with sixteen known alkaloids, were isolated from the whole plants of Corydalis edulis. The structures of the isolated alkaloids were established on the basis of extensive spectroscopic data (1D and 2D NMR, UV, IR, and HRESIMS). Their absolute configurations were determined by single-crystal X-ray crystallographic analysis and ECD. Compounds (+)-1 and (-)-1 are a pair of undescribed isoquinoline alkaloids bearing a unique coupled pattern of coptisine and ferulic acid via Diels-Alder [4 + 2] cycloaddition, while compounds (+)-2 and (-)-2 feature benzo [1,2-d:3,4-d]bis [1,3]dioxole moiety. Compounds (+)-2, (-)-2, (-)-5, 10, 13, 15, 20, 22, and 23 significantly triggered the secretion of insulin in the HIT-T15 cells at a concentration of 40 μM.

Concise synthesis of α-cyano tetrahydroisoquinolines with a quaternary center via Strecker reaction

A concise synthesis of α-cyano tetrahydroisoquinolines with a quaternary center via the Strecker reaction was successfully realized by employing TMSCN as cyano source and KF as fluoride source, furnishing the products with up to 99% yield. An isomerization of α-cyano tetrahydroisoquinoline was observed under alkaline conditions to give the isomer via [1,3]-H shift.

Concise synthesis of α-cyano tetrahydroisoquinolines with a quaternary center was successfully realized, furnishing products with up to 99% yield and an isomerization was observed under alkaline conditions, giving the isomer via [1,3]-H shift.

KF/Clinoptilolite Nanoparticles as a Heterogeneous Catalyst for Green Synthesis of pyrido[2,1-a]isoquinolines using Four-Component Reaction of Alkyl Bromides

OBJECTIVE

KF/Clinoptilolite nanoparticles are employed as a heterogeneous catalyst for the preparation of pyrido[2,1-a]isoquinoline derivatives through a four-component reaction of isoquinoline, two different alkyl bromides and an electron deficient internal alkynes at ambient temperature in water as green solvent.

METHODS

In this research, (2,2-Diphenyl-1-picrylhydrazyl) radical trapping and reducing potential of ferric ion experiments was used for determining antioxidant activity of some newly synthesized compounds such as 5a, 5c, 5f and 5g and comparing results with synthetic antioxidants (TBHQ and BHT).

RESULTS

Compounds 5a, 5c, 5f and 5g display trace DPPH radical trapping and excellent reducing power of ferric ion. Furthermore, the power of some prepared compounds against Gram-positive and Gram-negative bacteria was proved by employing the disk dispersion experiment.

CONCLUSION

The obtained results of disk diffusion test showed that compounds 5a, 5d and 5e prevented the bacterial growth. The reported procedure shows the advantages of clean reaction, high yield and simple purification.

Enzyme catalysed Pictet-Spengler formation of chiral 1,1'-disubstituted- and spiro-tetrahydroisoquinolines

The Pictet–Spengler reaction (PSR) involves the condensation and ring closure between a β-arylethylamine and a carbonyl compound. The combination of dopamine and ketones in a PSR leads to the formation of 1,1′-disubstituted tetrahydroisoquinolines (THIQs), structures that are challenging to synthesize and yet are present in a number of bioactive natural products and synthetic pharmaceuticals. Here we have discovered that norcoclaurine synthase from Thalictrum flavum (TfNCS) can catalyse the PSR between dopamine and unactivated ketones, thus facilitating the facile biocatalytic generation of 1,1′-disubstituted THIQs. Variants of TfNCS showing improved conversions have been identified and used to synthesize novel chiral 1,1′-disubstituted and spiro-THIQs. Enzyme catalysed PSRs with unactivated ketones are unprecedented, and, furthermore, there are no equivalent stereoselective chemical methods for these transformations. This discovery advances the utility of enzymes for the generation of diverse THIQs in vitro and in vivo.

The Pictet-Spengler condensation of β-arylethylamine and carbonyl compounds is an important step in the synthesis of bioactive alkaloids. Here, the authors report a Pictet-Spengler reaction between dopamine and unactivated ketones catalysed by norcoclaurine synthase and its engineered variants.

Simple and efficient synthesis of tetrahydro-β-carbolines via the Pictet–Spengler reaction in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)

1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) can act as both the solvent and the catalyst to effectively promote the Pictet–Spengler reaction.

Mild and efficient cyanuric chloride catalyzed Pictet-Spengler reaction

A practical, mild and efficient protocol for the Pictet–Spengler reaction catalyzed by cyanuric chloride (trichloro-1,3,5-triazine, TCT) is described. The 6-endo cyclization of tryptophan/tryptamine and modified Pictet–Spengler substrates with both electron-withdrawing and electron-donating aldehydes was carried out by using a catalytic amount of TCT (10 mol %) in DMSO under a nitrogen atmosphere. TCT catalyzed the Pictet–Spengler reaction involving electron-donating aldehydes in excellent yield. Thus, it has a distinct advantage over the existing methodologies where electron-donating aldehydes failed to undergo 6-endo cyclization. Our methodology provided broad substrate scope and diversity. This is indeed the first report of the use of TCT as a catalyst for the Pictet–Spengler reaction.

Heterogeneous Catalysts in Pictet-Spengler-Type Reactions

Several solid catalysts were evaluated as an alternative for 1,2,3,4-tetrahydroisoquinoline synthesis by means of the Pictet-Spengler reaction. The reaction catalysed by a mixed oxide (Mg and Al) led to the best yield and good regioselectivity; using an Al-pillared bentonite led to good yields and total regioselectivity. The results revealed no direct relationship between catalyst acidity and yield.

Scaffold-Directed Traceless Synthesis of Tetrahydro-β-carbolinehydantoins

Pharmacologically interesting tetrahydro-beta-carbolinehydantoins have been prepared through four-step traceless synthesis by a combinatorial approach. Two-arm PEG 1 (MW approximately 4000) was used as a soluble polymer support and reacted with Fmoc-protected L-tryptophane 2 to form bis-ester 3. The resulting polymer-supported amino ester 3 was deprotected, and amino ester 4 underwent Pictet-Spengler reaction with varoius ketones to form tricyclic indoles 5. The nucleophilic piperidine in the tricyclic indole reacted with isocyanate to generate the urea intermediates and simultaneously intramolecular cyclization to release the target compounds 7 from the support in good yields.