Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• compounds, including bioactive natural and nonnatural products, but also due to its impact on the discovery of pharmaceutical candidates and the total synthesis of intricate natural products. On the other hand, more recently, the field of photoredox catalysis has become an indispensable and unparalleled

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• products. Second, in order to be attractive for the total synthesis of relevant molecules, the involved EWG should preferably allow readily applicable and practicable postfunctionalizations [10]. Among the plethora of studied Michael acceptors, α,β-unsaturated aldehydes, thioesters, acylimidazoles, N

• , or trialkylaluminium reagents toward those challenging substrates and their fruitful application in the total synthesis of natural products. Review Enantioselective conjugate addition to challenging Michael acceptors Copper-catalyzed ECA to α,β-unsaturated aldehydes Nowadays, β-substituted enals

• ratios were obtained (51:49 to 97:3). Of note, chiral phosphines were also screened, but without any improvement of selectivity. Furthermore, this methodology was then efficiently applied to the total synthesis of several bisabolane sesquiterpenes, which exhibited anticancer and antimicrobial activities

Rapid, two-pot procedure for the synthesis of dihydropyridinones; total synthesis of aza-goniothalamin

• Thomas J. Cogswell,
• Craig S. Donald and
• Rodolfo Marquez

Beilstein J. Org. Chem. 2020, 16, 135–139, doi:10.3762/bjoc.16.15

• , three component coupling. Optimized conditions for the synthesis of diene 5. Ring-closing metathesis reaction of diene 5 to yield dihydropyridone 7 [20][21][22][23]. Total synthesis of aza-goniothalamin 1. Supporting Information Supporting Information File 218: Experimental, characterization data and

Convenient synthesis of the pentasaccharide repeating unit corresponding to the cell wall O-antigen of Escherichia albertii O4

• Tapasi Manna,
• Arin Gucchait and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2020, 16, 106–110, doi:10.3762/bjoc.16.12

• fragments with adequate purity. In this direction, the total synthesis of the pentasaccharide repeating unit corresponding to the cell wall O-antigenic polysaccharide of the E. albertii O4 strain using a sequential glycosylation strategy is presented herein (Figure 1). Results and Discussion The synthesis

Pigmentosins from Gibellula sp. as antibiofilm agents and a new glycosylated asperfuran from Cordyceps javanica

• Soleiman E. Helaly,
• Wilawan Kuephadungphan,
• Patima Phainuphong,
• Mahmoud A. A. Ibrahim,
• Kanoksri Tasanathai,
• Suchada Mongkolsamrit,
• Janet Jennifer Luangsa-ard,
• Souwalak Phongpaichit,
• Vatcharin Rukachaisirikul and
• Marc Stadler

Beilstein J. Org. Chem. 2019, 15, 2968–2981, doi:10.3762/bjoc.15.293

• ], invertebrate-pathogenic [38], and marine-derived [39] fungi, or even obtained by total synthesis [40][41][42], with diverse biological activities [40][41][43][44][45]. Nevertheless, the new compound, glycoasperfuran (3), was devoid of activity in all antimicrobial assays in spite of the fact that the

Terpenes

• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 2966–2967, doi:10.3762/bjoc.15.292

• elucidation, total synthesis, biosynthetic studies, bioactivity and functionalisation for mode of action studies, and other applications of terpenes, e.g. as fragrances. I thank all colleagues who have participated in this issue for their contributions and the whole Beilstein team for the professional support

Chemical synthesis of tripeptide thioesters for the biotechnological incorporation into the myxobacterial secondary metabolite argyrin via mutasynthesis

• David C. B. Siebert,
• Roman Sommer,
• Domen Pogorevc,
• Michael Hoffmann,
• Silke C. Wenzel,
• Rolf Müller and
• Alexander Titz

Beilstein J. Org. Chem. 2019, 15, 2922–2929, doi:10.3762/bjoc.15.286

• Saarbrücken, Germany 10.3762/bjoc.15.286 Abstract The argyrins are secondary metabolites from myxobacteria with antibiotic activity against Pseudomonas aeruginosa. Studying their structure–activity relationship is hampered by the complexity of the chemical total synthesis. Mutasynthesis is a promising

• , cytotoxicity and antibiotic activity, the selectivity profile of this class of compounds should be considered for optimization of future antibacterials. The first total synthesis was reported by Ley and co-workers [14] for argyrin B in 18 linear steps, followed by an alternative strategy towards argyrin F (6

• ) by the Kalesse group [15]. In 2011, Wu et al. reduced the length to 14 linear steps for the total synthesis of argyrins A and E [16]. Finally, Chen et al. described a synthesis yielding several derivatives of argyrin A with modification of the 4’-methoxytryptophan residue [17]. Changing the 4

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• significantly (Figure 8) [98]. Despite difficulties in engineering terpene biosynthesis, total synthesis of complex terpenoids does not appear to be a viable alternative. Traditionally, complex terpenes are synthesized from small and cheap chiral terpenes as starting material in (linear) multistep syntheses [99

• functionalization of nonactivated carbon atoms is one of the remaining challenges in organic synthesis [100][112][113]. Despite the progress made in total synthesis of terpenoids and the introduction of the two-phase mimicry of terpene biosynthesis during biomimetic syntheses, it has become obvious that total

• synthesis is currently not an efficient alternative to either the biotechnological production of terpenoids or the biosynthetic expansion of terpene chemical space [100][113]. Engineering terpene biosynthetic features to produce novel, non-natural terpenoids Terpene cyclases Most bacterial TCs produce one

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• in the synthesis of different complex and biologically relevant compounds as well as natural products. In 2008, Pilli and Santos developed an innovative method for the enantioselective total synthesis of the local anesthetic drug ropivacaine (197c) and its analogues levobupivacaine (197b) and

• -cyclodextrin as the cocatalyst provide 196 in a good yield and excellent stereoselectivity (Scheme 61). In 2011, Hurvois and his group reported a stereoselective electrochemical total synthesis of the tetrahydroisoquinoline alkaloid (−)-crispine A (200) and its natural enantiomer [108]. The initial steps

Safe and highly efficient adaptation of potentially explosive azide chemistry involved in the synthesis of Tamiflu using continuous-flow technology

• Cloudius R. Sagandira and
• Paul Watts

Beilstein J. Org. Chem. 2019, 15, 2577–2589, doi:10.3762/bjoc.15.251

• continuous-flow technology. The two steps involving azide chemistry in flow are reported herein (Scheme 2), with the vision of further integrating the other steps towards continuous-flow total synthesis of this drug. To this effect, we have already reported continuous flow shikimic acid (3) esterification

Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Escherichia coli O132 in the form of its 2-aminoethyl glycoside

• Debasish Pal and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2019, 15, 2563–2568, doi:10.3762/bjoc.15.249

• glycoside; diarrhea; galactofuranose; O-specific polysaccharide; total synthesis; Introduction O-Polysaccharides are the most complex molecular systems present in the bacterial cell wall owing to the presence of various sugar residues connected through diverse glycosidic linkages. These complex structures

• and Galf. In this communication we report on the total synthesis of this pentasaccharide repeating unit of the O-specific polysaccharide in the form of its 2-aminoethyl glycoside (Figure 1) through a [3 + 2] converging strategy. The building blocks were prepared by suitable protecting group

• reducing end of the target pentasaccharide that will allow further conjugation using the terminal amine without affecting the glycosidic stereochemistry. Further retrosynthetic analysis of the target pentasaccharide 1 revealed that a [3 + 2] strategy will be the most suitable one for the total synthesis of

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

• Benedikt C. Melzer,
• Alois Plodek and
• Franz Bracher

Beilstein J. Org. Chem. 2019, 15, 2304–2310, doi:10.3762/bjoc.15.222

• biosyntheses of known alkaloids, a “pyridoacridine family tree” which is claimed to be useful for designing total synthesis, but also for predicting yet undiscovered alkaloids from this chemotype [6]. Only two tricyclic benzo[c][2,7]naphthyridine alkaloids, perlolidine (6; from rye grass, Lolium perenne) [7

• , phenolates), acyl anions (generated by umpolung of aldehydes with imidazolium salts) and by palladium-catalyzed cross-coupling reactions (Suzuki, Stille) [10]. A related Stille cross coupling of a benzo[c][2,7]naphthyridine bearing a triflate group at C-5 gave an intermediate for the total synthesis of

• of the 4-bromo residue (cross-coupling reactions, nucleophilic substitutions) should open the opportunity to generate a broad variety of 4,5-disubstituted benzo[c][2,7]naphthyridines as building blocks for natural products total synthesis (Figure 2D). Results and Discussion For the envisaged direct

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• isolated from fungi of the genus Acremonium. Here, we present the asymmetric total synthesis of acremine F which hinges on a modestly enantioselective dihydroxylation and a subsequent kinetic resolution via a highly selective asymmetric reduction. Chemoselective oxidation of acremine F gave access to

• acremines A and B. The dimerization of acremine F to bisacremine E was investigated but could not be achieved, shedding light on the formation of the acremine dimers in nature. Keywords: meroterpenoid; natural product; selective oxidation; total synthesis; Introduction Endophytic fungi grow in a symbiotic

• transformation requires enzymatic catalysis in nature. Selected members of the acremine family [3][4][5]. Retrosynthetic analysis of acremine F (5). Total synthesis of acremine F (5). Synthesis of acremines A and B through selective oxidation of acremine F. Proposed biomimetic dimerization of 5. Attempted

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• al. developed a programmable enantioselective one-pot synthesis of molecules with eight stereocentres greatly improving the efficiency of natural product synthesis [83]. Each of these natural products are biologically active, hence their total synthesis will allow further characterisation of their

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• and multiple promising biological activities. In this review, progress in the total syntheses of triptolide are systematically summarized. We hope to gain a better understanding of the field and provide constructive suggestions for future studies of triptolide. Keywords: total synthesis; Tripterygium

• development of total synthesis strategies. Structurally, it has nine chiral centers, three successive epoxides and a butenolide. Since the pioneering works of Berchtold, Tahara and their co-workers [45][63][64][65], several racemic and/or asymmetric total syntheses of triptolide and its relatives have been

• carried out in many research groups. The first racemic total synthesis of triptolide was reported 1980 by Berchtold and co-workers (Figure 2, route A, and Scheme 1) [66]. The key steps include: i) construction of the A-ring by aldol condensation, ii) construction of the butenolide (D-ring) by acid

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• ,6S)-194a which appeared to be the enantiomer of natural microgrewiapine A although its structure was identical with the originally proposed. When the total synthesis started from the ester (2R,1'S)-5b and AD-mix-α was used the natural (+)-microgrewiapine A (2R,3S,6R)-194a was obtained. To synthesize

• (+)-deoxocassine ((2S,3S,6R)-190a) and (+)-spectaline ((2S,3S,6R)-190b) as already described. (+)-Microgrewiapine A ((2R,3S,6R)-194a) [107] and (+)-microcosamine A ((2R,3S,6R)-194b) [108] have recently been isolated and exhibited interesting biological activities, for example cytotoxicity [107]. The total

• synthesis of (−)-microgrewiapine A was initiated from the aziridine ketone 195 readily prepared from the ester (2S,1'R)-5b (Scheme 52) [109]. After chelation-controlled reduction of 195 with the NaBH4/ZnCl2 mixture and protection of a secondary alcohol the asymmetric dihydroxylation of the terminal C=C bond

Synthesis and biological evaluation of truncated derivatives of abyssomicin C as antibacterial agents

• Leticia Monjas,
• Peter Fodran,
• Johanna Kollback,
• Carlo Cassani,
• Thomas Olsson,
• Maja Genheden,
• D. G. Joakim Larsson and
• Carl-Johan Wallentin

Beilstein J. Org. Chem. 2019, 15, 1468–1474, doi:10.3762/bjoc.15.147

• benzyl group in the favorable subpocket position (Figure S1 in Supporting Information File 1). Synthesis The syntheses of 1 and 2 were inspired, in part, by previous strategies employed in the total synthesis of AbC [7][8][9][16][17]. Hence, the construction of the 11-membered ring was based on a

Efficiency Eff_syn of complex syntheses as multicomponent reactions, its algorithm and calculations based on concrete criteria

• Heiner Eckert

Beilstein J. Org. Chem. 2019, 15, 1425–1433, doi:10.3762/bjoc.15.142

• only show the synthesis path with the most spectacular molecules, such as the target molecule (TM), the total synthesis with all reactions is essential for production. The quantity of potential start molecule (STM) sets also rises strongly in complex syntheses. The example shows 5 STM sets (consisting

• (set-1) to which the parallel reactions are linked (set-2, set-3) is set up. The weighted arithmetical mean of the yields for each reaction set is formed at the connection forms. The overall yield yoa of the total synthesis is determined through the sequential operation of the main reaction sets. The

• values, together with the values from Π[Σ(Πyn)j]k, deliver the overall yield yoa of the total synthesis according to Equations 6–8. Parallel reactions set-2 to main reaction position (C), operation Σ(Πyn)j Parallel reactions set-3 to main reaction position (E), operation Σ(Πyn)j Sequential main reactions

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• corresponding 3° TBS ether) [14], and this strategy was subsequently also successfully applied in our most recent total synthesis of DDSQ (2) [13]. We now returned to study the Seebach alkylation chemistry in more detail. In 2008, Lipton and co-workers had observed that the cyclopentylidene derivative of

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

• Victoria V. Lipson,
• Tetiana L. Pavlovska,
• Nataliya V. Svetlichnaya,
• Anna A. Poryvai,
• Nikolay Yu. Gorobets,
• Erik V. Van der Eycken,
• Irina S. Konovalova,
• Svetlana V. Shiskina,
• Alexander V. Borisov,
• Vladimir I. Musatov and
• Alexander V. Mazepa

Beilstein J. Org. Chem. 2019, 15, 1032–1045, doi:10.3762/bjoc.15.101

• the disruptors of microtubule dynamics, therefore are of great interest in cancer drug discovery [6]. Thereby, the stereocontrolled total synthesis of marine alkaloids such as axinellamines [16] and the search of new 2-aminoimidazole and pyrrole containing compounds with a core structure that mimics

New terpenoids from the fermentation broth of the edible mushroom Cyclocybe aegerita

• Frank Surup,
• Florian Hennicke,
• Nadine Sella,
• Maria Stroot,
• Steffen Bernecker,
• Sebastian Pfütze,
• Marc Stadler and
• Martin Rühl

Beilstein J. Org. Chem. 2019, 15, 1000–1007, doi:10.3762/bjoc.15.98

• -H3 and 1-Hb indicated methyl C-12 being on the opposite site of the molecular plane as 2-H and 9-H. This assignment was confirmed by the comparison of the 13C NMR shifts to pasteurestin A and B [6][7]. Since the absolute stereochemistry has been demonstrated for pasteurestins A and B by total

• synthesis, we tentatively conclude a 2S,3R,8S,9R absolute configuration for pasteurestin C (4). The systematic name for 4 is (4S,4aR,7aS,7bR)-4-hydroxy-6,6,7b-trimethyl-2,4,4a,5,6,7,7a,7b-octahydro-1H-cyclobuta[e]indene-3-carboxylic acid. Bovistol A (1) showed weak cytotoxic effects (IC50 for L929 = 15 µg

Heck- and Suzuki-coupling approaches to novel hydroquinone inhibitors of calcium ATPase

• Robert J. Kempton,
• Taylor A. Kidd-Kautz,
• Soizic Laurenceau and
• Stefan Paula

Beilstein J. Org. Chem. 2019, 15, 971–975, doi:10.3762/bjoc.15.94

• tissues are avoided. Compound 1b was found to be selectively toxic to PSA-producing prostate cancer cells as well as in animal studies at submicromolar concentrations [3]. Unfortunately, TG has been difficult to obtain: extraction yields from natural sources are low and the total synthesis of TG required

Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 789–794, doi:10.3762/bjoc.15.75

• and was reported from different sources such as the liverwort Dumortiera hirsuta [19]. Its (Z)-configured exocyclic double bond has also attracted the attention of synthetic chemistry for a diastereoselective total synthesis [20][21][22]. The wide occurrence of 5 is likely connected to the simple

Synthesis of the polyketide section of seragamide A and related cyclodepsipeptides via Negishi cross coupling

• Jan Hendrik Lang and
• Thomas Lindel

Beilstein J. Org. Chem. 2019, 15, 577–583, doi:10.3762/bjoc.15.53

• product 30 carrying an 8-OPMP group was obtained from PMP-protected polyketide 28. The endgame of a total synthesis of seragamide A (2) will have to address the macrocyclisation, desilylation of the threonine moiety, and O-demethylation of the D-iodotyrosine unit of 31. In orienting reactions on small

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36