Total Synthesis of Pyrrole–Imidazole Alkaloid (+)-Cylindradine B

One-Pot Stereoselective Synthesis of the Naphthofurano-Iminosugars via a [3 + 2] Cycloaddition Reaction

This study presents the synthesis of novel naphthofurano-iminosugars (4) using 2,3-O-isopropylidene D-ribose tosylate (1a), anilines (2), and 1,4-benzoquinone (3a) as starting materials through key iminium ion/enamine intermediates via [3 + 2] cyclization reactions at room temperature. The reaction has unique regioselectivity and stereoselectivity with moderate to excellent yields. The adaptability of this method has been demonstrated using various substituted anilines, on which both electron-donating and electron-withdrawing groups were well employed in the reactions. Notably, the treatment of the fused multicyclic iminosugar 4 with TFA efficiently leads to an interesting unexpected pyridinium salt (8), possible via four sequential steps: deprotection of the 2,3-O-isopropylidene group, furan ring opening, dehydration condensation of the OH groups, and elimination of water.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Rh(III)-Catalyzed C-H Activation/Annulation of Benzohydroxamates and 2-Imidazolones: Access to Urea-Fused-Dihydroisoquinolone Scaffolds Reminiscent of Pyrrole Alkaloid Natural Products

A Rh(III)-catalyzed C-H activation/annulation with an imidazolone as alkene partner is reported to access dihydroisoquinolone-fused imidazolin-2-ones. These bicycles are reminiscent of scaffolds belonging to the pyrrole alkaloid family of natural products. This approach facilitates construction of a variety of urea-fused dihydroisoquinolone scaffolds including heterocyclic moieties.

Design and synthesis of novel benzimidazole-iminosugars linked a substituted phenyl group and their inhibitory activities against β-glucosidase

A series of novel benzimidazole-iminosugars linked a (substuituted) phenyl group on benzene ring of benzimidazole 5(a-p) and 6(a-p) have been rationally designed and conveniently synthesized through Suzuki coupling reaction in high yields. All compounds have been evaluated for their inhibitory activities against β-glucosidase (almond). Six compounds 5d, 6d, 6e, 6i, 6n, and 6p showed more significant inhibitory activities with IC₅₀ values in the range of 0.03-0.08 μM, almost 10-fold improved than that of the parent analogue 4, and much higher than that of the positive control castanospermine. The additional phenyl ring and the electron donating groups on it would be beneficial for the activity. Compounds 6d, 6n, and 4 had been chosen to be tested for their inhibition types against β-glucosidase. Interestingly, three compounds have different inhibition types although they had very similar structure. Their K_i values were calculated to be 0.02 ± 0.01 μM, 0.02 ± 0.01 μM, and 0.66 ± 0.14 μM, respectively. The equilibrium dissociation constant (K_D) for 6d, 6n, and 4 and β-glucosidase was 0.04 μM, 0.03 μM and 0.45 μM by the ITC-based assay, respectively. Molecular docking work suggests that such benzimidazole-iminosugars derivatives might bind to the active site of β-glucosidase mainly through hydrogen bonds, the additional phenyl ring towards the solvent-exposed region played an important effect on their inhibitory activity against β-glucosidase.

Efficient one-pot synthesis of the unexpected fused multicyclic iminosugars by an aza-Diels–Alder mechanism

A simple and efficient one-pot protocol has been developed by an aza-Diels–Alder mechanism for the stereoselective synthesis of novel fused multicyclic iminosugars with structural diversity.

Efficient construction of the hexacyclic ring core of palau'amine: the pK a concept for proceeding with unfavorable equilibrium reactions

Palau'amine has received a great deal of attention as an attractive synthetic target due to its intriguing molecular architecture and significant immunosuppressive activity, and we achieved its total synthesis in 2015. However, the synthesized palau'amine has not been readily applicable to the mechanistic study of immunosuppressive activity, because it requires 45 longest linear steps from a commercially available compound. Here, we report the short-step construction of the ABCDEF hexacyclic ring core of palau'amine. The construction of the CDE tricyclic ring core in a single step is achieved by our pK_a concept for proceeding with unfavorable equilibrium reactions, and a palau'amine analog without the aminomethyl and chloride groups is synthesized in 20 longest linear steps from the same starting material. The palau'amine analog is confirmed to retain the immunosuppressive activity. The present synthetic approach for a palau'amine analog has the potential for use in the development of palau'amine probes for mechanistic elucidation.

A palau'amine analog (2) was synthesized from 2-cyclopentenone in 20 steps. The construction of the CDE tricyclic ring core in a single step is achieved by our pK_a concept for proceeding with the unfavorable equilibrium reactions.

Marine Pyrrole Alkaloids

Nitrogen heterocycles are essential parts of the chemical machinery of life and often reveal intriguing structures. They are not only widespread in terrestrial habitats but can also frequently be found as natural products in the marine environment. This review highlights the important class of marine pyrrole alkaloids, well-known for their diverse biological activities. A broad overview of the marine pyrrole alkaloids with a focus on their isolation, biological activities, chemical synthesis, and derivatization covering the decade from 2010 to 2020 is provided. With relevant structural subclasses categorized, this review shall provide a clear and timely synopsis of this area.

Pyrrole carboxamide introduction in the total synthesis of pyrrole-imidazole alkaloids

In this review various strategies for the incorporation of the signature pyrrole carboxamide moiety in the total syntheses of pyrrole-imidazole alkaloids (PIA) are discussed. These so-called oroidin alkaloids have a broad range of biological activities and display interesting skeletal diversity and complexity. These alkaloids are sponge-derived secondary metabolites and thus far more than 200 members of the PIA family have been isolated over the past few decades. Methods range from classical amide bond forming processes to non-traditional bond formation including the de novo synthesis of the pyrrole itself.

N,N-Diacylaminals as Emerging Tools in Synthesis: From Peptidomimetics to Asymmetric Catalysis

N,N-Diacylaminals are flexible molecular scaffolds that have commonly been utilized as amide surrogates in peptidomimetics. The singularities of this motif as an N-acyl imine equivalent and as hydrogen-bond donor have recently opened new synthetic opportunities, especially in the field of asymmetric catalysis. This concept article highlights this diverse synthetic potential and provides the elements necessary for further developments.

Recent progress in the total synthesis of pyrrole-containing natural products (2011–2020)

This review discusses total syntheses of pyrrole-containing natural products over the last ten years, highlighting recent advances in the chemistry of pyrroles in the context of their innate reactivity, and their preparation in complex settings.

The chemistry and biology of guanidine secondary metabolites

Covering: 2017-2019Guanidine natural products isolated from microorganisms, marine invertebrates and terrestrial plants, amphibians and spiders, represented by non-ribosomal peptides, guanidine-bearing polyketides, alkaloids, terpenoids and shikimic acid derived, are the subject of this review. The topics include the discovery of new metabolites, total synthesis of natural guanidine compounds, biological activity and mechanism-of-action, biosynthesis and ecological functions.

One-pot synthesis of substituted pyrrole-imidazole derivatives with anticancer activity

A facile and efficient method to synthesize pyrrole-imidazole was developed via a post-Ugi cascade reaction followed by one purification procedure. Synthesized pyrrole-imidazole was collected by performing a mild reaction and a simple procedure, which could be applicable to a broad scope of functionalized anilines. The screening results demonstrated that compound 7e exhibited a high potency of anticancer activity in human pancreatic cancer cell lines PANC and ASPC-1. Our work shed light on the potential of post-Ugi cascade reaction in combinatorial and medicinal chemistry.

Synthesis of tricyclic quinazolinone-iminosugars as potential glycosidase inhibitors via a Mitsunobu reaction

A series of novel tricyclic quinazolinone-iminosugars 1 (a-c) were synthesized from the benzyl protected sugars through three steps. Firstly, the benzyl protected sugar (aldehyde) 5 reacted with o-aminobenzamide by the iodine-induced oxidative condensation to afford the corresponding aldo-quizanolinone 6. Secondly, through the intramolecular cyclization of the unprotected OH and the amide NH in 6, the tricyclic compounds 7 and 8 were constructed by the key Mitsunobu reaction. Finally, removal of the benzyl group gave the target tricyclic quinazolinone-iminosugars 1. The protocol was effective for the preparation of the tricyclic iminosugars in satisfactory yield. Interestingly, an unusual C-2 epimerization was observed with d-mannose and d-ribose compounds under the conditions of the Mitsunobu reaction that generated the products having the trans configuration at the C-2 and C-3 positions. Unfortunately, such tricyclic quinazolinone-iminosugars showed no inhibitory effects on the tested five glycosidases.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.

Recent synthetic applications of α-amido sulfones as precursors of N-acylimino derivatives

α-Amido sulfones can be directly used as N-acylimine or N-acyliminium ion precursors in several synthetic processes aimed at the preparation of nitrogen containing compounds. This review collects the most relevant and practical utilizations of α-amido sulfones appeared in the literature after 2005.