The ethoxycarbonyl group as both activating and protective group in N-acyl-Pictet–Spengler reactions using methoxystyrenes. A short approach to racemic 1-benzyltetrahydroisoquinoline alkaloids

• Marco Keller,
• Karl Sauvageot-Witzku,
• Franz Geisslinger,
• Nicole Urban,
• Michael Schaefer,
• Karin Bartel and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2716–2725, doi:10.3762/bjoc.17.183

• ][4][5]. In continuation of our recent work on the chemistry and pharmacology of benzylisoquinolines and related compounds [6][7][8][9][10][11][12][13][14] we investigated truncated analogues of the bisbenzylisoquinoline alkaloid tetrandrine as blockers of the calcium channel two-pore channel 2 (TPC2

• by lithium alanate reduction [18][19]. In a novel total synthesis of the racemic alkaloid N-methylcoclaurine (1) performed in this course we also used the ethoxycarbonyl group successfully for protection of two phenolic groups at two different rings during the N-acyl-Pictet–Spengler reaction [15

• comparison to tetrandrine and cepharanthine, we performed Ca2+ measurements in multiwell plates. Therefore, heterologously TPC2-expressing HEK293 cells were loaded with calcium indicator fluo-4/AM and Ca2+ entry was measured for 5 min after injection of various alkaloid concentrations (0.1–100 µM). None of

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• derivatives, phase-transfer catalysts and bifunctional thiourea derivatives. 1.1 Reactions catalyzed by chiral cinchona alkaloid derivatives Cai et al. prepared and used a number of organocatalysts from Cinchona alkaloids for the aza-MR of aniline (1) with chalcone (2) to obtain the adducts 4 in poor to very

• derivatives. It was perceived that the MDO self-assembled in situ from amino acids and cinchona alkaloid derivatives. For example, on reacting (E)-2-[2-(3-aryl-3-oxoprop-1-en-1-yl)phenyl]acetaldehydes 21 with ethyl or benzyl (E)-2-[(4-methoxyphenyl)imino]acetates 22 in the presence of the MDO 23/24

• cinchona alkaloid-derived quaternary ammonium salts (cat. 55) as the phase-transfer catalyst. The products were obtained in high yields (53–93%) with high enantioselectivities (40–76% ee) (Table 12) [46]. Lebrun et al. developed a new method to synthesize optically active isoindolinones via asymmetric

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• cyclobutane derivatives (Figure 21b), highlighting the importance of the relief of ring strain in driving the rearrangement [31]. Like their α‑ketol counterparts, rearrangements of α‑iminols have also been used in total syntheses. In their total synthesis of four eburnane-type alkaloid natural products 122

• produces 119. b) Cyclopentanone-based substrates (120) do not react under the same conditions. Four eburnane-type alkaloid natural products 122–125 were synthesized from common intermediate 127, which was produced from known precursor 126 by an α-iminol rearrangement.

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• pomegranate alkaloid punicagranine (5) (Figure 1) [5]. The 2,3-dihydro-1H-pyrrolizine motif is also a structural component of potential drugs with a variety of pharmacological effects [6], including anticancer activity [7]. Relevant examples include (−)-ketorolac (6) [8], which has reached the market as a

• natural products, there is considerable synthetic potential in the transformation. Application of the methods described herein to the synthesis of lamellarin alkaloid analogues will be reported in due course. Examples of 2,3-dihydro-1H-pyrrolizines (1–7) and 5,6,7,8-tetrahydroindolizines (8–10). Previous

Base-free enantioselective S_N2 alkylation of 2-oxindoles via bifunctional phase-transfer catalysis

• Mili Litvajova,
• Emiliano Sorrentino,
• Brendan Twamley and
• Stephen J. Connon

Beilstein J. Org. Chem. 2021, 17, 2287–2294, doi:10.3762/bjoc.17.146

• investigation by evaluating, as a model alkylation, the phase-transfer-catalysed benzylation of substrate 5 under ‘classical’ basic reaction conditions using cinchona alkaloid-based catalysts capable of hydrogen-bonding as a control element [33][34][35][36][37][38][39][40]. As expected, the ester group α to the

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• the indoles are less studied compared to the same through their pyrrole counterpart. The corresponding compounds are investigated for boron, nitrogen, oxygen, sulfur, and selenium as the central connecting atom. Boranes The indole alkaloid dragmacidin D is a marine secondary metabolite which was

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• enantioselective Michael addition of ketones 20 to 3-aroylcoumarins 19 [38]. For this transformation, the authors used a cinchona alkaloid-derived primary amine catalyst 22 (Scheme 6a). The study was performed with cyclic and acyclic ketones 20 and various 3-aroylcoumarins 19 and the desired products 21 were

• discussed above, the organocatalysts may also proceed by noncovalent activation, in which a hydrogen bond or an ion pair is formed. A broad variety of mono- and bifunctional chiral hydrogen-bonding organocatalysts has been developed, in special using cinchona alkaloid derivatives [52]. In this sense, Lin

• reaction between 4-hydroxycoumarins 1 and aromatic imines 63 for the synthesis of α-benzylaminocoumarins 64 [54]. Among the cinchona alkaloid derivatives evaluated in this reaction, cupreine (65) was found to be the best option in terms of yields and enantioselectivities (Scheme 20). Both electron

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• phenanthroindolizidine alkaloid boehmeriasin A (31) (Scheme 12A) [98], and phenanthroindolizidines through an intramolecular oxidative aryl–alkene coupling (Scheme 12B) [99], which is a far less common transformation in organic synthesis. This approach was employed to synthesize eight phenanthroindolizidines, including

• present in the natural product bismurrayafoline E (36) [105], an alkaloid found in the leaves of Murraya koeniggi (Scheme 13D) [106]. The oxidative formation of carbon–carbon bonds mediated by vanadium has been reported as a method for the aminomethylation of arenes and heteroarenes. The so far described

Natural products in the predatory defence of the filamentous fungal pathogen Aspergillus fumigatus

• Jana M. Boysen,
• Nauman Saeed and
• Falk Hillmann

Beilstein J. Org. Chem. 2021, 17, 1814–1827, doi:10.3762/bjoc.17.124

• (19) is a tryptophan-derived indole alkaloid which was so far only shown to be produced by A. fumigatus while other fumigaclavines can for example also be found in Penicillium ssp. (fumigaclavine A (18) and B (17)) [66][158]. In all fungi, alkaloid biosynthetic pathways share a common basis, starting

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• ’-difluorobipyridinium salts and N,N’-difluoro-1,4-diazoniabicyclo[2.2.2]octane salts, and their many derivatives and analogs, including chiral N-F reagents such as optically active N-fluoro-sultam derivatives, N-fluoro-alkaloid derivatives, DABCO-based N-F derivatives, and N-F binaphthyldisulfonimides. The synthesis

• (entry 6, Figure 9), it was less than that obtained (74% ee) by N-fluorosultam (R)-27-6 with the same substrate (see the previous section 1-27). 1-29. N-Fluorinated cinchona alkaloid derivatives by combination with Selectfluor In 2000, Shibata and Takeuchi reported a far more practical enantioselective

• fluorination method. They discovered that the fluorination of carbanions with Selectfluor occurred in a highly enantioselective manner when carried out in the presence of cinchona alkaloid derivatives [95]. This method consisted of two simple steps. Firstly, the cinchona alkaloid is reacted with Selectfluor in

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• -pyrido[3,4-b]indole (β-carboline) is the most naturally abundant, present for instance, in the alkaloid harmine, a well-known selective inhibitor of monoamine oxidase-A (MAO-A) [1]. On the contrary, 5H-pyrido[4,3-b]indoles (γ-carbolines) are comparatively less examined, although these heterocycles have

• shown promising biological activities in preclinical and clinical studies (Figure 1) [2][3][4][5][6]. The pyrimidine-γ-carboline alkaloid ingenine B (isolated from an Indonesian sponge) exhibits a pronounced cytotoxicity against a murine lymphoma cell line [7] and several isocanthine analogs are

• alkaloid ingenine B [20]. The iodine-catalyzed [3 + 3] cycloaddition of indolyl alcohol to enaminones [21] and the thiourea-catalyzed iso-Pictet–Spengler reaction of isotryptamine with aldehydes [22], are some noteworthy contributions to the field. A cascade or domino reaction is an interesting approach

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• , his Introduzione allo Studio degli Alcaloidi con special riguardo agli alcaloidi vegetali ed alle ptomaine (An Introduction to Alkaloid Chemistry, and especially on those of plant origin and on ptomaines), first published in 1892, was translated four years later into German, and the popularity of this

• work is testified by Willstätter, who in his memoirs refers to Guareschi as “alkaloid chemist” [28]. Ptomaines (from the Greek πτωμα, cadaver) are anaerobic bacterial degradation products of proteins and choline-containing phospholipids. The formation of these is associated with putrefaction of animal

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• derivative 57 in 72% combined yield (Scheme 18) [88]. In 2020, Pierce and co-workers developed a method for the synthesis of guanidinium alkaloid batzelladine D in enantiomeric and racemic form, along with a series of stereochemical analogues. The batzelladines are a family of polycyclic guanidinium

• )2] in DMF was the best to produce lactams 77. The synthetic interest of these functionalized lactams was demonstrated in the synthesis of alkaloid (−)-preussin (78) from the appropriate precursor 77 in three steps (Scheme 23). Similar strategies were employed to obtain similar heterocycles [99

• straightforward synthesis of the alkaloid (−)-pelletierine (112) was accomplished by the diastereoselectivity coupling of 3-oxobutanoic acid (110) and the N-tert-butanesulfinyl imine (RS)-109 derived from 5-bromopentanal (114). The base-promoted decarboxylative-Mannich coupling of these reagents led to β-amino

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

• Takashi Nishiyama,
• Erina Hamada,
• Daishi Ishii,
• Yuuto Kihara,
• Nanase Choshi,
• Natsumi Nakanishi,
• Mari Murakami,
• Kimiko Taninaka,
• Noriyuki Hatae and
• Tominari Choshi

Beilstein J. Org. Chem. 2021, 17, 730–736, doi:10.3762/bjoc.17.62

• , Yokohama University of Pharmacy, 601 Matano, Totsuka-ku, Yokohama 245-0066, Japan 10.3762/bjoc.17.62 Abstract The first total synthesis of the pyrrolo[2,3-c]quinoline alkaloid trigonoine B (1) was accomplished via a six-step sequence involving the construction of an N-substituted 4-aminopyrrolo[2,3-c

• structures of the compounds were elucidated through 1D and 2D NMR spectroscopy. It was determined that trigonoine A was a β-carboline alkaloid containing a 2,8-diazabicyclo[3.3.1]nonane ring system, while trigonoine B (1) was formed by a combination of 2,3-dihydroquinolin-4-one and 3H-pyrrolo[2,3-c]quinoline

• acquired physical and spectroscopic data of the herein synthesized compound 1 were consistent with those of the natural trigonoine B [1]. Thus, in this study, we successfully achieved the first total synthesis of trigonoine B (1). Conclusion The total synthesis of a pyrrolo[2,3-c]quinoline alkaloid

The synthesis of chiral β-naphthyl-β-sulfanyl ketones via enantioselective sulfa-Michael reaction in the presence of a bifunctional cinchona/sulfonamide organocatalyst

• Deniz Tözendemir and
• Cihangir Tanyeli

Beilstein J. Org. Chem. 2021, 17, 494–503, doi:10.3762/bjoc.17.43

• Deniz Tozendemir Cihangir Tanyeli Department of Chemistry, Middle East Technical University, 06800 Ankara, Turkey 10.3762/bjoc.17.43 Abstract Cinchona alkaloid-derived organocatalysts are widely employed in various asymmetric transformations, yielding products with high enantiopurity. In this

• transition state model to explain the origin of the stereoinduction was proposed (Scheme 2), according to the Houk’s Brønsted acid hydrogen bonding model. Guo’s computational work in 2017 on the sulfa-Michael addition of thiols to enones in the presence of cinchona alkaloid-type organocatalysts showed that

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• methodology followed by NaBH4 reduction. This structure with three condensed rings can be seen as a new class of unnatural, chiral alkaloid scaffolds, potentially exhibiting pharmacological activity (Scheme 3) [40]. Various unsuccessful attempts were made to deprotect compound 3e. Unexpectedly, however, one of

• couplings and NOE effects shown. Our previous efforts in the field of functionalization of sugar-derived lactams. Preliminary experiment in search of a procedure for the synthesis of 2-(1H-tetrazol-5-yl)-iminosugars. Synthesis of a new class of alkaloid scaffold using the presented methodology. Synthesis of a

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• ), isolated from the Colorado blue spruce Picea pungens, are members of this alkaloid family. Their unique bicyclic system with a quaternary stereocenter, and the potent biological activity exerted by these homotropane alkaloids, make them attractive synthetic targets. This work aims briefly to review the

• ] and [3.2.2] (Figure 1). The homotropane alkaloid (−)-adaline (1) was isolated from ladybird Adalia bipunctata [17] and Cryptolaemus moutrouzieri secretions [18]. A methyl analog, (+)-euphococcinine (2), has been found in vegetable and animal kingdoms. The compound was first isolated from the

• Australian coastal plant Euphorbia atoto [19], and it is also present in the defense secretion of ladybirds Cryptolaemus montrouzieri [18] and Epilachna varivestis [16]. Also, (+)-N-methyleuphococcinine (3) has been identified as a trace homotropane alkaloid isolated from the spruce tree Picea pungens [20

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• last, carbazole-based heterohelicenes were found in nature, for example, purpurone [55] isolated from the marine sponge Iotrochota sp. and having an inhibitory effect on the ATP-citrate lyase, and the marine alkaloid ningalin D produced by Didemnum sp., Dictyodendrins [56] isolated from Dictyodendrilla

An atom-economical addition of methyl azaarenes with aromatic aldehydes via benzylic C(sp³)–H bond functionalization under solvent- and catalyst-free conditions

• Divya Rohini Yennamaneni,
• Vasu Amrutham,
• Krishna Sai Gajula,
• Rammurthy Banothu,
• Murali Boosa and
• Narender Nama

Beilstein J. Org. Chem. 2020, 16, 3093–3103, doi:10.3762/bjoc.16.259

• diversity, these compounds constitute a motif in various natural alkaloid products, such as chimanine and those derived from lobelia, sedum, etc. These compounds act as anti-HIV and anti-asthma drugs [9][10][11]. Mainly, 2-substituted quinolines and their analogues exhibits magnificent bioactivity [12][13

Synthesis and investigation of quadruplex-DNA-binding, 9-O-substituted berberine derivatives

• Jonas Becher,
• Daria V. Berdnikova,
• Heiko Ihmels and
• Christopher Stremmel

Beilstein J. Org. Chem. 2020, 16, 2795–2806, doi:10.3762/bjoc.16.230

• successfully developed as G4-DNA ligands [17], the natural product berberine (1a) has attracted special attention. Berberine (1a) is an isoquinoline alkaloid with an exceptionally wide range of biological activities [23][24]. It has been shown that berberine (1a) and its derivatives act, for example, as anti

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

• Florian Mann,
• Daiane Szczerbowski,
• Lisa de Silva,
• Melanie McClure,
• Marianne Elias and
• Stefan Schulz

Beilstein J. Org. Chem. 2020, 16, 2776–2787, doi:10.3762/bjoc.16.228

• contained ithomiolide A (3), a pyrrolizidine alkaloid derived γ-lactone, I. s. derasa carried the sesquiterpene α-elemol (8) in the androconia. These differences might be important for the reproductive isolation of the two subspecies, in line with previously reported low gene exchange between the two

• various plants [9]. These alkaloids are transformed into the alkaloid and pheromone precursor lycopsamine (1, Scheme 1) [10][11][12] that can then be converted either into necine base derived compounds such as methyl hydroxydanaidoate (2), or into necic acids derived ones, e.g., ithomiolide A (3) [10][11

• -hydroxy-11-octadecenoate; Y: methyl 3-hydroxyoctadecanoate; E: (E)-isomer of (R)-25. The enantiomer (S,E)-25 elutes together with (R,Z)-25, indicated by the broader base of this peak in B compared to C. Pyrrolizidine alkaloid lycopsamine (1) and the putative pheromone compounds methyl hydroxydanaidoate (2

Controlling the stereochemistry in 2-oxo-aldehyde-derived Ugi adducts through the cinchona alkaloid-promoted electrophilic fluorination

• Yuqing Wang,
• Gaigai Wang,
• Anatoly A. Peshkov,
• Ruwei Yao,
• Muhammad Hasan,
• Manzoor Zaman,
• Chao Liu,
• Stepan Kashtanov,
• Olga P. Pereshivko and
• Vsevolod A. Peshkov

Beilstein J. Org. Chem. 2020, 16, 1963–1973, doi:10.3762/bjoc.16.163

• alkaloid-promoted electrophilic fluorination producing enantioenriched post-Ugi adducts fluorinated at the peptidyl position. Keywords: cinchona alkaloids; electrophilic fluorination; enantioselective synthesis; 2-oxo-aldehydes; Ugi reaction; Introduction Multicomponent reactions (MCRs) [1][2][3][4][5][6

• carbonyl compounds promoted by cinchona alkaloid derivatives developed independently by Shibata, Takeuchi and co-workers [65][66] and by the group of Cahard [67][68][69][70]. The method proved to be applicable to a broad range of substrates under a variety of conditions [71][72][73][74][75][76][77][78] and

• , a cinchona alkaloid derivative was allowed to react with an electrophilic fluorinating agent to afford an N-fluoroammonium salt of the cinchona alkaloid via transfer fluorination. In the second step, the Ugi adduct 8a was added to this in situ generated N-fluorocinchona intermediate to afford the

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• [42][43][44][45][46]. In our research endeavors, we have been involved in the exploration of the synthetic potential of 1-formyl-9H-β-carboline (an alkaloid, kumujian C) [47] for preparing chemical libraries of β-carboline-substituted [48][49][50][51][52][53][54] and N-fused heterocycles [55][56

• a one-pot metal-free approach for the first time. The transformation could be executed from β-carboline-based 2-nitrochalcones via a one-pot, two-step procedure starting from 1(3)-formyl-β-carbolines (a framework represented by alkaloid kumujian C). The combination of Et3N and DMSO played a vital

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• quantities of cobalt present in the reaction mixture. The same group also studied the intramolecular PKR of chiral fluorine-containing N-tethered 1,7-enynes 48 for the stereoselective construction of enantioenriched bicyclic alkaloid analogues 49, containing a fluorine atom in the bridge position [61]. For

Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells

• Giacomo Mari,
• Lucia De Crescentini,
• Serena Benedetti,
• Francesco Palma,
• Stefania Santeusanio and
• Fabio Mantellini

Beilstein J. Org. Chem. 2020, 16, 1606–1616, doi:10.3762/bjoc.16.133

• Molecular Biology, Department of Biomolecular Sciences, University of Urbino “Carlo Bo”, Via Saffi 2, 61029 Urbino, Italy 10.3762/bjoc.16.133 Abstract Dihydroberberine (DHBER), the partially reduced form of the alkaloid berberine (BER), is known to exhibit important biological activities. Despite this fact

• various inflammatory diseases. The main component of this rhizome is berberine (BER), an alkaloid with numerous pharmacological properties, which include anticancer and anti-inflammatory activities [1]. However, the low bioavailability, poor solubility, and moderate nucleic acid binding affinity

• activity [13][14][15][16][17][18][19], and an increased DNA and RNA binding efficacy [4][6][9], due to its aromatic interactions with the biological macromolecules [20]. Another interesting and promising derivative is dihydroberberine (DHBER), the reduced form of BER. The enaminic function of this alkaloid