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Organic & Biomolecular Chemistry

Yingyi Duan, Yanyan Liu, Tao Huang, Yi Zou, Tingting Huang, Kaifeng Hu, Zixin Deng, Shuangjun Lin
FR900452 and spirocyclic maremycins, including F and G components, are structurally related indole alkaloids, previously identified from different Streptomyces species. These alkaloids feature an indole diketopiperazine motif linked with a cyclopentenone moiety, but the linkage differs in FR900452 and the spirocyclic maremycins. Here, FR900452 and its two new analogues were identified from the fermentation broth of Streptomyces sp. B9173, the producer of maremycins. Gene inactivation and heterologous expression of the mar gene cluster confirmed that production of FR900452 shares the same biosynthetic machinery that produces maremycins...
July 18, 2018: Organic & Biomolecular Chemistry
Luisa Lempenauer, Aline Soupart, Elisabet Duñach, Gilles Lemière
A straightforward two-step entry to α-oxgenated β,γ-unsaturated ketones from readily available α,β-unsaturated ketones is disclosed. It was found that bis(allylic) alcohols undergo a skeletal rearrangement in the presence of 1 mol% of cheap and non-corrosive p-toluenesulfonic acid. Computational studies were conducted to support the mechanism and to rationalise the influence of the catalyst acidity on the product selectivity.
July 18, 2018: Organic & Biomolecular Chemistry
Ze-Lin Li, Kang-Kang Sun, Chun Cai
A cobalt-catalyzed regioselective C-H halogenation methodology is reported herein. The highlight of this work is the highly selective C-H functionalization of anilides, which results in high-yielding, versatile, and practical halogenated products. Thereby, brominations, chlorinations and iodinations of many electron-rich and electron-deficient anilides were achieved in a highly selective fashion. Mechanistic studies with respect to the pathway of the reaction are also described.
July 18, 2018: Organic & Biomolecular Chemistry
Eva Schütznerová, Adam Přibylka, Viktor Krchňák
Fmoc-protected Nα-amino acid containing heterocyclic privileged structures, O-(1-methyl-5-oxo-2,5-dihydro-1H-pyrrol-3-yl)-l-serine and O-((S)-5-oxo-2,3,5,7a-tetrahydro-1H-pyrrolizin-7-yl)-l-serine, were synthesized on the solid phase from simple commercially available building blocks under mild conditions. The amino acid side-chain is composed of tetramic acid, a natural product derived privileged structure. The key transformation was the formation of cyclic enol ethers via nonclassical Wittig olefinations of the esters...
July 17, 2018: Organic & Biomolecular Chemistry
Jonathan D Bell, Alexander H Harkiss, Christopher R Wellaway, Andrew Sutherland
An acid-mediated 6-endo-trig cyclisation of amine-substituted enones has been developed for the stereoselective synthesis of trans-6-alkyl-2-methyl-4-oxopiperidines. Performed under conditions that prevent removal of the Boc-protecting group or acetal formation, the key cyclisation was found to generate cleanly the 4-oxopiperidine products in high overall yields from a wide range of alkyl substituted enones. The synthetic utility of the trans-6-alkyl-2-methyl-4-oxopiperidines formed from this process was demonstrated with the total synthesis of the quinolizidine alkaloid, (+)-myrtine and the piperidine alkaloid, (-)-solenopsin A...
July 16, 2018: Organic & Biomolecular Chemistry
Erik M Larsen, Chia-Fu Chang, Tomoyo Sakata-Kato, Joseph W Arico, Vince M Lombardo, Dyann F Wirth, Richard E Taylor
The synthesis of a 2-methyl-substituted analogue of the natural product, neopeltolide, is reported in an effort to analyze the importance of molecular conformation and ligand-target interactions in relation to biological activity. The methyl substitution was incorporated via highly diastereoselective ester enolate alkylation of a late-stage intermediate. Coupling of the oxazole sidechain provided 2-methyl-neopeltolide and synthetic neopeltolide via total synthesis. The substitution was shown to maintain the conformational preferences of its biologically active parent compound through computer modeling and NMR studies...
July 16, 2018: Organic & Biomolecular Chemistry
Eva J van Rooden, Roy Kreekel, Thomas Hansen, Antonius P A Janssen, Annelot C M van Esbroeck, Hans den Dulk, Richard J B H N van den Berg, Jeroen D C Codée, Mario van der Stelt
Diacylglycerol lipases (DAGL) produce the endocannabinoid 2-arachidonoylglycerol, a key modulator of neurotransmitter release. Chemical tools that visualize endogenous DAGL activity are desired. Here, we report the design, synthesis and application of a triazole urea probe for DAGL equipped with a norbornene as a biorthogonal handle. The activity and selectivity of the probe was assessed with activity-based protein profiling. This probe was potent against endogenous DAGLα (IC50 = 5 nM) and it was successfully applied as a two-step activity-based probe for labeling of DAGLα using an inverse electron-demand Diels-Alder ligation in living cells...
July 13, 2018: Organic & Biomolecular Chemistry
Ting-Ting Xu, Tao-Shan Jiang, Xiao-Lan Han, Yuan-Hong Xu, Jin-Ping Qiao
An efficient synthesis of (E)-cinnamaldehydes by a metal-free DDQ-mediated oxidative transformation of allylarenes was developed. The protocol provides a practical method to prepare diverse (E)-cinnamaldehydes with broad functional group tolerance in good to excellent yields, including easy access to natural products randainal and geranyloxy sinapyl aldehyde from plant extracts. Finally, the mechanism of a single-electron transfer process was proposed.
July 13, 2018: Organic & Biomolecular Chemistry
Fang Yuan, Yuan Tian, Weirong Qin, Jingxu Li, Dan Yang, Bingchuan Zhao, Feng Yin, Zigang Li
Antimicrobial peptides (AMPs) are short cationic peptides with a high affinity for membranes and emerged as a promising therapeutic approach with potential for treating infectious diseases. Chemical stabilization of short peptides proved to be a successful approach for enhancing their bio-physical properties. Herein, we designed and synthesized a panel of conformationally constrained antimicrobial peptides with either α-helical or β-hairpin conformation using templating strategies. These synthetic short constrained peptides possess different topological distributions of hydrophobic and hydrophilic residues and displayed distinct antimicrobial activity...
July 13, 2018: Organic & Biomolecular Chemistry
Yin-Hui Huang, Xian-Yi Jin, Yong-Yi Zhao, Hang Cong, Zhu Tao
A selective and sensitive fluorescent chemosensor based on an anthracene-functionalized triazole-linked multifarene[2,2] was successfully synthesized and investigated with regard to the recognition of metal ions using fluorescence spectroscopy, 1H NMR titration, and IR spectroscopy. The proposed sensor exhibited desirable properties for potential fluorescence enhanced chemosensor applications, including selective affinity and low Zn2+ and Cd2+ detection limits compared with other metal ions. Quantum chemical calculations described the synthesized chemosensor's static structure and its coordination to Zn2+ and Cd2+...
July 12, 2018: Organic & Biomolecular Chemistry
Yading Hou, Yuwen Zhang, Xiaofeng Tong
The first example of phosphine-catalyzed α-umpolung addition of nucleophiles to allenoates is described, which features the use of δ-acetoxy allenoate to generate a 3-phosphonium-2,4-dienoate intermediate, thus facilitating the α-umpolung addition of nucleophiles. Both sulfinate and diarylphosphine oxide are competitive nucleophiles, affording highly activated conjugated dienes with good to excellent stereoselectivities.
July 12, 2018: Organic & Biomolecular Chemistry
N Esmati, A R Maddirala, N Hussein, H Amawi, A K Tiwari, P R Andreana
A one-pot, two-step, total synthesis of naturally occurring xenortides A, B, C and D, (Xens A-D) isolated from the bacterium Xenorhabdus nematophila, and an entire complementary set of stereoisomers, has been achieved. Compounds were synthesized utilizing an isocyanide-based Ugi 4-CR followed by facile N-Boc deprotection. The reaction sequence took advantage of the chiral pool of N-Boc protected amino acids (l-Leu/Val and d-Leu/Val) with aryl isocyanides, phenyl acetaldehyde and methylamine giving the desired Xens A-D (A and B >98% ee) and all subsequent stereoisomers in reasonable yields upon deprotection followed by separation of diastereomers...
July 12, 2018: Organic & Biomolecular Chemistry
Jing Yan, Chengbu Liu, Dongju Zhang
This work presents a computational study of RhIII-catalyzed synthesis of 1,2-benzothiazines from NH-sulfoximines and diazo compounds reported by Bolm et al. (Angew. Chem., Int. Ed., 2015, 54, 12349). The reaction involves five sequent processes: elimination of dinitrogen, C-H activation, carbene insertion, protonation, and dehydration, and the C-H activation is identified as the rate-determining step with a barrier of 33.1 kcal mol-1. Phenyl sulfoximine is found to be the most favorable substrate with the lowest barrier in comparison with methoxybenzene sulfoximine and nitrobenzene sulfoximine...
July 12, 2018: Organic & Biomolecular Chemistry
Peng An, Qing Lin
A panel of sterically shielded tetrazoles with different N-aryl groups were synthesized and subsequently evaluated in the photoinduced tetrazole-alkene cycloaddition reaction. It was found that increase in the HOMO energy of the corresponding nitrile imines leads to a faster cycloaddition reaction along with a red shift in the fluorescence emission of the pyrazoline cycloadduct.
July 11, 2018: Organic & Biomolecular Chemistry
Sheng Zhang, Hengmin Ma, Hon Eong Ho, Yoshinori Yamamoto, Ming Bao, Tienan Jin
A new and efficient Pd-catalyzed cascade cyclization of biaryl-tethered o-alkynylanilines for the formation of dibenzo[a,c]carbazole derivatives has been reported. The use of the alkyl-substituted tertiary anilines together with the combination of the PdCl2 catalyst with the MnO2 oxidant and PivOH is vital for giving rise to 5-endo cyclization, C-N bond cleavage, and C-H bond activation in a cascade manner to produce the corresponding products with structural diversity.
July 11, 2018: Organic & Biomolecular Chemistry
Marcus Wegmann, Michael Henkel, Thorsten Bach
The Catellani reaction enables an ortho-C-H activation based on oxidative addition of Pd(0) and an intermediary carbopalladation of norbornene. Among its variants, the recently developed C2-selective alkylation of indoles is particular as it employs Pd(ii) as the source of palladium. This review describes the mechanistic background of this transformation. Applications in total synthesis and in the synthesis of biologically relevant molecules are illustrated and further developments of the method are discussed...
July 11, 2018: Organic & Biomolecular Chemistry
Samuel D Griggs, Daniel T Tape, Paul A Clarke
Spiropiperidines have gained in popularity in drug discovery programmes as medicinal chemists explore new areas of three-dimensional chemical space. This review focuses on the methodology used for the construction of 2-, 3- and 4-spiropiperidines, covering the literature from the last 10 years. It classifies the synthesis of each of the types of spiropiperidine by synthetic strategy: the formation of the spiro-ring on a preformed piperidine ring, and the formation of the piperidine ring on a preformed carbo- or heterocyclic ring...
July 11, 2018: Organic & Biomolecular Chemistry
Leo Corcilius, Dennis Y Liu, Jessica L Ochoa, Roger G Linington, Richard J Payne
The glycinocins are a class of calcium-dependent, acidic cyclolipopeptide antibiotics that are structurally related to the clinically approved antibiotic daptomycin. In this article, we describe the synthesis of a small library of glycinocin analogues that differ by variation in the exocyclic fatty acyl substituent. The glycinocin analogues were screened against a panel of Gram-positive bacteria (as well as Gram-negative P. aeruginosa). These analogues exhibited similar calcium-dependent activity to the parent natural products against Gram-positive bacteria but showed no activity against P...
July 11, 2018: Organic & Biomolecular Chemistry
Ramanathan Devenderan, Pitchumani Kasi
A novel, metal-free, base promoted sp2 C-H functionalization in the sulfonamidation of 1,4-naphthoquinones via a [3 + 2] cycloaddition reaction using sulfonyl azides under mild reaction conditions is reported. In this straightforward atom- and step-economical protocol, the active alkene moiety of quinone undergoes a thermal azide-alkene [3 + 2] cycloaddition followed by proton abstraction, ring opening and elimination of a nitrogen molecule to form sulfonamidation products in good yield and all the synthesized sulfonamidation derivatives exhibit good absorption and emission characteristics...
July 11, 2018: Organic & Biomolecular Chemistry
Abdul Rahman, Qiaoxia Zhou, Xufeng Lin
A highly efficient synthesis of chiral 3,3-disubstituted oxindoles was developed using a chiral spirocyclic phosphoric acid catalyzed 1,6-conjugate addition reaction of para-quinone methides derived from N-unprotected isatins with indoles. The reaction proceeds under mild reaction conditions to provide indole-containing N-unprotected oxindoles bearing quaternary stereocenters in good yields and with moderate to excellent enantioselectivities (up to 97% ee).
July 11, 2018: Organic & Biomolecular Chemistry
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