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• 525-41-7 1-methyl-4,9-dihydro-3H-β-carboline 
• 16502-01-5 tetrahydrobetacarboline 
• 1198364-39-4 C₂₉H₃₆N₂O₂ 
• 1198364-49-6 C₂₅H₂₈N₂O₂ 
• 2506-10-7 eleagnine 
• 16308-68-2 allyl phenyl carbonate 
• 343-94-2 tryptamine hydochloride 
• 75-07-0 acetaldehyde 
• 486-84-0 harmane 
• 6678-82-6 (+/-)-Calligonine hydrochloride 
• 1016-47-3 N-Acetyltryptamine 
• 61-54-1 tryptamine 
• 142605-15-0 (1R,1'R)-9-benzyl-2-(2-hydroxy-1-phenylethyl)-1-methyl-1,2,3,4-tetrahydropyrido<3,4-b>indole 
• 125923-35-5 methyl (N¹-benzyl-3-indolyl)acetate 

Relevant academic research and scientific papers

Inverted Binding of Non-natural Substrates in Strictosidine Synthase Leads to a Switch of Stereochemical Outcome in Enzyme-Catalyzed Pictet-Spengler Reactions

The Pictet-Spengler reaction is a valuable route to 1,2,3,4-tetrahydro-β-carboline (THBC) and isoquinoline scaffolds found in many important pharmaceuticals. Strictosidine synthase (STR) catalyzes the Pictet-Spengler condensation of tryptamine and the aldehyde secologanin to give (S)-strictosidine as a key intermediate in indole alkaloid biosynthesis. STRs also accept short-chain aliphatic aldehydes to give enantioenriched alkaloid products with up to 99% ee STRs are thus valuable asymmetric organocatalysts for applications in organic synthesis. The STR catalysis of reactions of small aldehydes gives an unexpected switch in stereopreference, leading to formation of the (R)-products. Here we report a rationale for the formation of the (R)-configured products by the STR enzyme from Ophiorrhiza pumila (OpSTR) using a combination of X-ray crystallography, mutational, and molecular dynamics (MD) studies. We discovered that short-chain aldehydes bind in an inverted fashion compared to secologanin leading to the inverted stereopreference for the observed (R)-product in those cases. The study demonstrates that the same catalyst can have two different productive binding modes for one substrate but give different absolute configuration of the products by binding the aldehyde substrate differently. These results will guide future engineering of STRs and related enzymes for biocatalytic applications.

Bifunctional thiosquaramide catalyzed asymmetric reduction of dihydro-β-carbolines and enantioselective synthesis of (-)-coerulescine and (-)-horsfiline by oxidative rearrangement

Tetrahydro-β-carboline (THBC) is a tricyclic ring system that can be found in a large number of bioactive alkaloids. Herein, we report a simple and efficient method for the synthesis of enantiopure THBCs through a chiral thiosquaramide (11b) catalyzed imine reduction of dihydro-β-carbolines (17a-f). The in situ generated Pd-H employed as hydride source in the reaction of differently substituted chiral THBCs (18a-f) afforded high selectivities (R isomers, up to 96% ee) and good isolated yields (up to 88%). Moreover, the chiral thiosquaramide used also afforded exceptional catalyst activity in the syntheses of (-)-coerulescine (5) and (-)-horsfiline (6) with excellent enantioselectivities up to 98% and 93% ee, respectively, via an enantioselective oxidative rearrangement approach.

Sequence-Based In-silico Discovery, Characterisation, and Biocatalytic Application of a Set of Imine Reductases

Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine-forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence-based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates. Specific activities of >1 U/mg and excellent stereoselectivities (ee>99 %) were observed in many cases, and the enzymes proved surprisingly tolerant towards elevated substrate loadings. Co-expression of the IREDs with an alcohol dehydrogenase for cofactor regeneration led to whole-cell biocatalysts capable of efficiently reducing imines at 100 mM initial concentration with no need for the addition of extracellular nicotinamide cofactor. Preparative biotransformations on gram scale using these ‘designer cells’ afforded chiral amines in good yield and excellent optical purity.

(-)-Menthol as a source of new N,N-diamine ligands for asymmetric transfer hydrogenation

The synthesis of new chiral N-monotosylated-1,2-diamines based on the (-)-menthol skeleton is presented. The elimination of HCl from neomenthyl chloride obtained from an Appel reaction led to p-menth-3-ene in excellent yield. Further functionalization of the double bond in p-menth-3-ene with chloramine-T gave the corresponding N-tosylaziridines, which upon reaction with sodium azide and subsequent reduction of the azide functional group, formed the 1,2-diamine system. The synthesized chiral ligands proved effective in the asymmetric transfer hydrogenation of aromatic ketones and an endocyclic imine.

Exploiting the Catalytic Diversity of Short-Chain Dehydrogenases/Reductases: Versatile Enzymes from Plants with Extended Imine Substrate Scope

Numerous short-chain dehydrogenases/reductases (SDRs) have found biocatalytic applications in C=O and C=C (enone) reduction. For NADPH-dependent C=N reduction, imine reductases (IREDs) have primarily been investigated for extension of the substrate range. Here, we show that SDRs are also suitable for a broad range of imine reductions. The SDR noroxomaritidine reductase (NR) is involved in Amaryllidaceae alkaloid biosynthesis, serving as an enone reductase. We have characterized NR by using a set of typical imine substrates and established that the enzyme is active with all four tested imine compounds (up to 99 % conversion, up to 92 % ee). Remarkably, NR reduced two keto compounds as well, thus highlighting this enzyme family's versatility. Using NR as a template, we have identified an as yet unexplored SDR from the Amaryllidacea Zephyranthes treatiae with imine-reducing activity (≤95 % ee). Our results encourage the future characterization of SDR family members as a means of discovering new imine-reducing enzymes.

Candida antarctica lipase B catalysed kinetic resolution of 1,2,3,4-tetrahydro-?-carbolines: Substrate specificity

In the frame of substrate specificity, CAL-B-catalysed asymmetric N-alkoxycarbonylations of 1-substituted tetrahydro-?-carbolines (Me, Et, Pr, iPr) have been studied. High enantioselectivities (>200) were observed, when alkoxycarbonylation of racemic compounds (±)-1,3,5,7 were performed in DIPE in the presence of phenyl allyl carbonate and Et3N at 60 °C using ultrasound shaking method. The reaction time increased considerably with increasing substituent size on C1; however, the isopropyl-substituted compound proved to be too bulky for the optimum activity of CAL-B. The (R)-carbamate enantiomers were hydrolysed using Pd2(dba)3.CHCl3 and the enantiomers of the free amines were obtained with excellent ee (>99%).

Asymmetric Synthesis of (R)-1-Alkyl-Substituted Tetrahydro-?-carbolines Catalyzed by Strictosidine Synthases

Stereoselective methods for the synthesis of tetrahydro-?-carbolines are of significant interest due to the broad spectrum of biological activity of the target molecules. In the plant kingdom, strictosidine synthases catalyze the C?C coupling through a Pictet–Spengler reaction of tryptamine and secologanin to exclusively form the (S)-configured tetrahydro-?-carboline (S)-strictosidine. Investigating the biocatalytic Pictet–Spengler reaction of tryptamine with small-molecular-weight aliphatic aldehydes revealed that the strictosidine synthases give unexpectedly access to the (R)-configured product. Developing an efficient expression method for the enzyme allowed the preparative transformation of various aldehydes, giving the products with up to >98 % ee. With this tool in hand, a chemoenzymatic two-step synthesis of (R)-harmicine was achieved, giving (R)-harmicine in 67 % overall yield in optically pure form.

Efficient lipase-catalysed route for the kinetic resolution of salsolidine and its ?-carboline analogue

Racemic 1-methyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline 1 and 1-methyl-1,2,3,4-tetrahydro-?-carboline 3 were resolved through lipase-catalysed asymmetric acylation on the secondary amino group. High enantioselectivities (E >200) were observed when t

Enantioselective hydrogenation of cyclic imines catalysed by Noyori-Ikariya half-sandwich complexes and their analogues

A method for enantioselective hydrogenation of cyclic imines with gaseous hydrogen has been developed. Easily accessible Noyori-Ikariya Ru(ii) and Rh(iii) complexes can be used directly without an inert atmosphere. Substrate activation has been achieved by trifluoroacetic acid. A new hydroxyl-functionalized complex is reported, showing high activity in transfer hydrogenation.

Stereoselectivity and Structural Characterization of an Imine Reductase (IRED) from Amycolatopsis orientalis

The imine reductase AoIRED from Amycolatopsis orientalis (Uniprot R4SNK4) catalyzes the NADPH-dependent reduction of a wide range of prochiral imines and iminium ions, predominantly with (S)-selectivity and with ee's of up to >99%. AoIRED displays up to 100-fold greater catalytic efficiency for 2-methyl-1-pyrroline (2MPN) compared to other IREDs, such as the enzyme from Streptomyces sp. GF3546, which also exhibits (S)-selectivity, and thus, AoIRED is an interesting candidate for preparative synthesis. AoIRED exhibits unusual catalytic properties, with inversion of stereoselectivity observed between structurally similar substrates, and also, in the case of 1-methyl-3,4-dihydroisoquinoline, for the same substrate, dependent on the age of the enzyme after purification. The structure of AoIRED has been determined in an "open" apo-form, revealing a canonical dimeric IRED fold in which the active site is formed between the N- and C-terminal domains of participating monomers. Co-crystallization with NADPH gave a "closed" form in complex with the cofactor, in which a relative closure of domains, and associated loop movements, has resulted in a much smaller active site. A ternary complex was also obtained by cocrystallization with NADPH and 1-methyl-1,2,3,4-tetrahydroisoquinoline [(MTQ], and it reveals a binding site for the (R)-amine product, which places the chiral carbon within 4 ? of the putative location of the C4 atom of NADPH that delivers hydride to the C? -N bond of the substrate. The ternary complex has permitted structure-informed mutation of the active site, resulting in mutants including Y179A, Y179F, and N241A, of altered activity and stereoselectivity.