Methylerythritol Phosphate Pathway: Enzymatic Evidence for a Rotation in the LytB/IspH-Catalyzed Reaction

IspH/LytB, an oxygen-sensitive [4Fe-4S] enzyme, catalyzes the last step of the methylerythritol phosphate (MEP) pathway, a target for the development of new antimicrobial agents. This metalloenzyme converts (E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate (HMBPP) into the two isoprenoid precursors: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Here, the synthesis of (S)-[4-²H₁]HMBPP and (R)-[4-²H₁]HMBPP is reported together with a detailed NMR analysis of the products formed after their respective incubation with E. coli IspH/LytB in the presence of the biological reduction system used by E. coli to reduce the [4Fe-4S] center. (S)-[4-²H₁]HMBPP was converted into [4-²H₁]DMAPP and (E)-[4-²H₁]IPP, whereas (R)-[4-²H₁]HMBPP yielded [4-²H₁]DMAPP and (Z)-[4-²H₁]IPP, hence providing the direct enzymatic evidence that the mechanism catalyzed by IspH/LytB involves a rotation of the CH₂OH group of the substrate to display it away from the [4Fe-4S].     

Structure elucidation of four prenylindole derivatives from Streptomyces sp. isolated from Ailuropoda melanoleuca feces

Four new prenylindole derivatives, (R)‐6‐(2,3‐dihydroxy‐3‐methylbutyl)indole (1), (R)‐6‐(2,3‐dihydroxy‐3‐methylbutyl)indolin‐2‐one (2), and an unseparated mixture of (Z)‐6‐(4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl)indolin‐2‐one (3a) and (E)‐6‐(4‐hydroxy‐3‐methylbut‐2‐en‐1‐yl)indolin‐2‐one (3b) with a ratio of 3 : 2, were isolated from the culture broth of a streptomycete isolated from Ailuropoda melanoleuca feces. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic techniques. The absolute configuration of 1 was determined by Mosher's method. Copyright © 2013 John Wiley & Sons, Ltd.     

A Facile Cell Free Synthesis of Isotopically Labeled (E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl Diphosphate,a Precursor of the Plant Hormone Zeatin

(E)‐4‐Hydroxy‐3‐methylbut‐2‐enyl diphosphate ( 1 ) is a key intermediate of the deoxyxylulose phosphate pathway of isoprenoid biosynthesis and a precursor of the plant hormone zeatin. The availability of this intermediate with various labeling patterns is pivotal for its use in biosynthetic studies. The number of positions, however, that can be easily labeled by chemical synthesis is limited, and the synthesis by means of recombinant enzymes is laborious and time consuming. We demonstrated that chromoplasts from Capsicum annuum, whose enzyme activity was impaired by freeze‐thawing, accumulate 1 . This observation built the basis for the development of a cell‐free system allowing the synthesis of this intermediate with labels in various positions. With 2C‐methyl‐D ‐erythritol 2,4‐cyclodiphosphate ( 5 ) as substrate, yields were in the range of 50%.     

Bisabolane Derivatives from Leontopodium alpinum

From the roots of Leontopodium alpinum, four new bisabolane sesquiterpenoids, (1R*,2S*,4R*,5S*)‐4‐(acetyloxy)‐2‐[3‐(acetyloxy)‐1,5‐dimethylhex‐4‐enyl]‐5‐methylcyclohexyl (2Z)‐2‐methylbut‐2‐enoate ( 1 ), (1R*,4S*,6R*)‐4‐(acetyloxy)‐6‐[3‐(acetyloxy)‐1,5‐dimethylhex‐4‐enyl]‐3‐methylcyclohex‐2‐en‐1‐yl (2Z)‐2‐methylbut‐2‐enoate ( 2 ), and 3‐methyl‐1‐{2‐[(1R*,2R*,5R*,6S*)‐2,5,6‐tris(acetyloxy)‐4‐methylcyclohex‐3‐en‐1‐yl]propyl}but‐2‐enyl (2Z)‐2‐methylbut‐2‐enoate ( 3 and 4 ) have been isolated. The latter constituents differ from each other by the relative configurations of the chiral centers of the hexenyl side chain.     

Three New Phthalides from Gnaphalium adnatum

Three new phthalides, gnaphalides A–C ( 1 – 3 , resp.), together with three known phthalides, were isolated from the aerial part of Gnaphalium adnatum. The structures of the new compounds were elucidated as 6‐(1,1‐dimethylprop‐2‐en‐1‐yl)‐5,7‐dihydroxy‐2‐benzofuran‐1(3H)‐one ( 1 ), 5‐hydroxy‐7‐[(2‐hydroxy‐3‐methylbut‐3‐en‐1‐yl)oxy]‐2‐benzofuran‐1(3H)‐one ( 2 ), and 1,3‐dihydro‐7‐[(3‐methylbut‐2‐en‐1‐yl)oxy]‐1‐oxo‐2‐benzofuran‐5‐yl β‐D ‐glucopyranoside ( 3 ) on the basis of spectral analyses. The structure of 1 was also confirmed by X‐ray crystallographic analysis. The three known phthalides, identified as 5,7‐dihydroxyisobenzofuran‐1(3H)‐one ( 4 ), anaphatol ( 5 ), and 7‐O‐(β‐glucopyranosyl)‐5‐hydroxyisobenzofuran‐1(3H)‐one ( 6 ), were isolated from the genus Gnaphalium for the first time.     

New Long‐Chain Esters and Adenine Analogs from the Leaves of Formosan Bridelia balansae

Six new compounds, including the two long‐chain esters balansenate I (=6,8,11‐trimethyldodecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 1 ) and balansenate II (=10,12,15‐trimethylhexadedecanoic acid (2E)‐3‐methylhexadec‐2‐enyl ester; 2 ), the eburicane‐like triterpenoid bridelone (=hexadecahydro‐4,4,10,13,14‐pentamethyl‐17‐(5‐methyl‐1,4‐dimethylenehexyl)‐3H‐cyclopenta[a]phenanthren‐3‐one; 3 ), the ‘deimino‐xanthine', bridelonine (=5‐(3‐methylbut‐2‐enyl)pyrrolo[3,4‐d]imidazole‐4,6(1H,5H)‐dione; 6 ), and the two adenine analogs 9‐(3‐methylbut‐2‐enyl)adenine ( 7 ) and 1‐(3‐methylbut‐2‐enyl)adenine ( 8 ), besides three known compounds, i.e., N⁶‐(3‐methylbut‐2‐enyl)adenine ( 4 ), 3‐(3‐methylbut‐2‐enyl)adenine ( 5 ), and adenine ( 9 ), were isolated from the leaves of Formosan Bridelia balansae. The novel skeleton of 6 consists of a fused pyrrolidine‐2,5‐dione and imidazole moiety. The already known adenines 7 and 8 were isolated for the first time from a plant. The structures of the isolated compounds were elucidated by spectroscopic analyses.     

Paecilomycines A and B,Novel Diterpenoids,Isolated from Insect‐Pathogenic Fungi Paecilomyces sp. ACCC 37762

Two new diterpenoids, named paecilomycine A ( 1 ) and paecilomycine B ( 2 ), including a novel skeleton with a five‐membered lactone ring, together with three known labdane diterpenoids, rel‐(1R,3S,4aS,5R,8aS)‐5‐[(3E)‐4‐carboxy‐3‐methylbut‐3‐en‐1‐yl]decahydro‐3‐hydroxy‐1,4a‐dimethyl‐6‐methylidenenaphthalene‐1‐carboxylic acid ( 3 ), botryosphaerin E ( 4 ), and agathic acid ( 5 ), were isolated from solid culture of the insect pathogenic fungi strain Paecilomyces sp. The structures of all compounds were established on the basis of comprehensive spectroscopic studies. The relative configurations of 1 and 2 were determined by single‐crystal X‐ray diffraction analyses.     

Three‐dimensional hydrogen‐bonded framework structures in flunarizinium nicotinate and flunarizinediium bis(4‐toluenesulfonate) dihydrate

The structures of two salts of flunarizine, namely 1‐bis[(4‐fluorophenyl)methyl]‐4‐[(2E)‐3‐phenylprop‐2‐en‐1‐yl]piperazine, C₂₆H₂₆F₂N₂, are reported. In flunarizinium nicotinate {systematic name: 4‐bis[(4‐fluorophenyl)methyl]‐1‐[(2E)‐3‐phenylprop‐2‐en‐1‐yl]piperazin‐1‐ium pyridine‐3‐carboxylate}, C₂₆H₂₇F₂N₂⁺·C₆H₄NO₂⁻, (I), the two ionic components are linked by a short charge‐assisted N—H...O hydrogen bond. The ion pairs are linked into a three‐dimensional framework structure by three independent C—H...O hydrogen bonds, augmented by C—H...π(arene) hydrogen bonds and an aromatic π–π stacking interaction. In flunarizinediium bis(4‐toluenesulfonate) dihydrate {systematic name: 1‐[bis(4‐fluorophenyl)methyl]‐4‐[(2E)‐3‐phenylprop‐2‐en‐1‐yl]piperazine‐1,4‐diium bis(4‐methylbenzenesulfonate) dihydrate}, C₂₆H₂₈F₂N₂²⁺·2C₇H₇O₃S⁻·2H₂O, (II), one of the anions is disordered over two sites with occupancies of 0.832 (6) and 0.168 (6). The five independent components are linked into ribbons by two independent N—H...O hydrogen bonds and four independent O—H...O hydrogen bonds, and these ribbons are linked to form a three‐dimensional framework by two independent C—H...O hydrogen bonds, but C—H...π(arene) hydrogen bonds and aromatic π–π stacking interactions are absent from the structure of (II). Comparisons are made with some related structures.     

Isolation of a New Carotenoid and Two New Carotenoid Glycosides from Curtobacterium flaccumfaciens pvar poinsettiae

An efficient method for the extraction of the carotenoids from Curtobacterium flaccumfaciens pvar poinsettiae was developed. The glucosides of C.p. 450 (=(all‐E,2R,2′R)‐2‐[4‐(β‐D ‐glucopyranosyloxy)‐3‐methylbut‐2‐enyl]‐2′‐(4‐hydroxy‐3‐methylbut‐2‐enyl)‐β, β‐carotene; 4 ) and of C.p. 473 (=(all‐E,2R,2′S)‐2‐[4‐(β‐D ‐glucopyranosyloxy)‐3‐methylbut‐2‐enyl]‐2′‐(3‐methylbut‐2‐enyl)‐3′,4′‐didehydro‐1′,2′‐dihydro‐β,ψ‐caroten‐1′‐ol; 5 ) were isolated for the first time. In addition, the hitherto unknown 3′,4′‐dihydro derivative of C.p. 450, called C.p. 460 (=(all‐E,2R,2′R)‐2‐(4‐hydroxy‐3‐methylbut‐2‐enyl)‐2′‐(3‐methylbut‐2‐enyl)‐1′,2′‐dihydro‐β,ψ‐caroten‐1′‐ol; 6 ), was identified. The structures were established by UV/VIS, CD, ¹H‐ and ¹³C‐NMR, and mass spectra.     

An efficient synthesis of 5‐aryl‐4,5‐dihydro‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐1‐(4‐phenylthiazol‐2‐yl)pyrazoles

Some new target products 5‐aryl‐4,5‐dihydro‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐1‐(4‐phenylthiazol‐2‐yl)pyrazoles 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j have been synthesized by reaction of 2‐bromo‐1‐phenylethanone and compounds 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j which were prepared from the combination of thiosemicarbazide and (E)‐3‐aryl‐1‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐prop‐2‐en‐1‐ones 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j . All the structures were established by MS, IR, CHN, and ¹H NMR spectra data. Synthesis of structure diversity is applied. J. Heterocyclic Chem., (2011).     

Synthesis of some new 1‐acyl‐5‐aryl‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐4,5‐dihydro‐1H‐pyrazole

Some new compounds (E)‐3‐aryl‐1‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐prop‐2‐en‐1‐ones 5a–e were prepared by 1‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐ethanone and various aromatic aldehydes. Then one pot reaction was happened by compounds 5a–e with hydrazine hydrate in acetic acid or propionic acid, respectively, to give the title compounds 1acyl‐5‐aryl‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐4,5‐dihydro‐1H‐pyrazoles 6a–i . All structures were established by MS, IR, CHN, ¹H‐NMR and ¹³C‐NMR spectral data. J. Heterocyclic Chem., (2012).     

Enantioselective Addition of Cyclic Enol Silyl Ethers to 2‐Alkenoyl‐Pyridine‐N‐Oxides Catalysed by CuII–Bis(oxazoline) Complexes

Asymmetric reactions involving (E)‐3‐aryl‐1‐(pyridin‐2‐yl‐N‐oxide)prop‐2‐en‐1‐ones and cyclic enol silyl ethers show good yields and excellent enantioselectivities (up to 99.9 % ee) when catalysed by bis(oxazoline)–Cu^II complexes. Different reaction pathways can be followed by different enol silyl ethers: with 2‐(trimethylsilyloxy)furan, a Mukaiyama–Michael adduct is obtained, whereas a hetero Diels–Alder cycloadduct was formed by using (1,2‐dihydronaphthalen‐4‐yloxy)trimethylsilane. In the latter reaction, the absolute configuration of the product is consistent with a reagent approach to the less hindered Re face of the coordinated substrate in the reactive complex.     

Synthesis and Antimicrobial Screening of Some Novel 2‐(5‐(4‐(1H‐Benzo[d][1,2,3]triazol‐1‐yl)phenyl)‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenols Incorporated by Triazole Moiety

A novel series of 2‐(5‐(4‐(1H‐benzo[d][1,2,3]triazol‐1‐yl)phenyl)‐4,5‐dihydro‐1H‐pyrazol‐3‐yl)phenols derivative has been synthesized from (E)‐3‐(4‐(1H‐benzo[d][1,2,3]triazol‐1‐yl)phenyl)‐1‐(2‐hydroxyphenyl)prop‐2‐en‐1‐ones in ethanol and hydrazine hydrate under reflux condition. The synthesized compounds were screened for antibacterial activity against Gram‐positive bacteria viz Staphylococcus aureus and Bacillus subtilis and Gram‐negative bacteria viz Escherichia coli and Salmonella typhi, respectively. Some of the tested compounds showed significant antimicrobial activity. IR, ¹H NMR, mass spectral data, and elemental analysis elucidated the structures of all the newly synthesized compounds.     

New Chemical Constituents from Borreria verticillata (Rubiaceae)

A phytochemical study on Borreria verticillata has led to the isolation of two novel simple indole alkaloids, 6‐methoxy‐4‐(3‐methylbut‐2‐en‐1‐yl)‐1H‐indole, named verticillatine A ( 1 ), and 1‐(1H‐indol‐6‐yl)‐3‐methylbutan‐1‐one, named verticillatine B ( 2 ), one new iridoid, 6′‐O‐(2‐glyceryl)scandoside methyl ester ( 3 ), with the glycerol unit linked to a glucose unit, and two known ones, asperuloside ( 4 ) and scandoside methyl ester ( 5 ). The structures of these compounds were elucidated on the basis of spectroscopic‐data analyses, mainly ¹H‐ and ¹³C‐NMR, including 2D experiments (¹H,¹H‐COSY, NOESY, HMBC, and HMQC), and HR‐ESI‐MS.     

Two novel organic–inorganic hybrid materials from tetrachloridometallate(II) salts and 4‐[(E)‐2‐(pyridin‐1‐ium‐2‐yl)ethenyl]pyridinium

Two organic–inorganic hybrid compounds have been prepared by the combination of the 4‐[(E)‐2‐(pyridin‐1‐ium‐2‐yl)ethenyl]pyridinium cation with perhalometallate anions to give 4‐[(E)‐2‐(pyridin‐1‐ium‐2‐yl)ethenyl]pyridinium tetrachloridocobaltate(II), (C₁₂H₁₂N₂)[CoCl₄], (I), and 4‐[(E)‐2‐(pyridin‐1‐ium‐2‐yl)ethenyl]pyridinium tetrachloridozincate(II), (C₁₂H₁₂N₂)[ZnCl₄], (II). The compounds have been structurally characterized by single‐crystal X‐ray diffraction analysis, showing the formation of a three‐dimensional network through X—H...Cl_nM⁻ (X = C, N⁺; n = 1, 2; M = Co^II, Zn^II) hydrogen‐bonding interactions and π–π stacking interactions. The title compounds were also characterized by FT–IR spectroscopy and thermogravimetric analysis (TGA).     

Insights into the Synthesis of Steroidal A‐Ring Olefins

The classical synthesis, followed by purification of the steroidal A‐ring Δ¹‐olefin, 5α‐androst‐1‐en‐17‐one ( 5 ), from the Δ¹‐3‐keto enone, (5α,17β)‐3‐oxo‐5‐androst‐1‐en‐17‐yl acetate ( 1 ), through a strategy involving the reaction of Δ¹‐3‐hydroxy allylic alcohol, 3β‐hydroxy‐5α‐androst‐1‐en‐17β‐yl acetate ( 2 ), with SOCl₂, was revisited in order to prepare and biologically evaluate 5 as aromatase inhibitor for breast cancer treatment. Surprisingly, the followed strategy also afforded the isomeric Δ²‐olefin 6 as a by‐product, which could only be detected on the basis of NMR analysis. Optimization of the purification and detection procedures allowed us to reach 96% purity required for biological assays of compound 5 . The same synthetic strategy was applied, using the Δ⁴‐3‐keto enone, 3‐oxoandrost‐4‐en‐17β‐yl acetate ( 8 ), as starting material, to prepare the potent aromatase inhibitor Δ⁴‐olefin, androst‐4‐en‐17‐one ( 15 ). Unexpectedly, a different aromatase inhibitor, the Δ^3,5‐diene, androst‐3,5‐dien‐17‐one ( 12 ), was formed. To overcome this drawback, another strategy was developed for the preparation of 15 from 8 . The data now presented show the unequal reactivity of the two steroidal A‐ring Δ¹‐ and Δ⁴‐3‐hydroxy allylic alcohol intermediates, 3β‐hydroxy‐5α‐androst‐1‐en‐17β‐yl acetate ( 2 ) and 3β‐hydroxyandrost‐4‐en‐17β‐yl acetate ( 9 ), towards SOCl₂, and provides a new strategy for the preparation of the aromatase inhibitor 12 . Additionally, a new pathway to prepare compound 15 was achieved, which avoids the formation of undesirable by‐products.     

Hydrogen phosphate and dihydrogen phosphate salts of 4‐amino­azobenzene

4‐Amino‐trans‐azobenzene {or 4‐[(E)‐phenyl­diazen­yl]aniline} can form isomeric salts depending on the site of protonation. Both orange bis{4‐[(E)‐phenyl­diazen­yl]anilinium} hydrogen phos­phate, 2C₁₂H₁₂N₃⁺·HPO₄²⁻, and purple 4‐[(E)‐phenyl­diazen­yl]­anilinium dihydrogen phosphate phosphoric acid solvate, C₁₂H₁₂N₃⁺·H₂PO₄⁻·H₃PO₄, (II), have layered structures formed through O—H⋯O and N—H⋯O hydrogen bonds. Additionally, azobenzene fragments in (I) are assembled through C—H⋯π inter­actions and in (II) through π–π inter­actions. Arguments for the colour difference are tentatively proposed.     

Synthesis of Dihydropyrans and Dihydrofurans via Radical Cyclization of Unsaturated Alcohols and 1,3‐Dicarbonyl Compounds

The oxidative cyclization reactions of 1,3‐dicarbonyl compounds 1a – 1c and α,β‐unsaturated alcohols 2a – 2f with Mn(OAc)₃ were performed, leading to dihydrofurans. Treatment of 1a and 1b with 2‐methylbut‐3‐en‐2‐ol ( 2a ) gave dihydrofurans 3aa and 3ba , and dihydropyrans 4aa and 4ba , as unexpected products. While the reaction of 2‐methylbut‐3‐yn‐2‐ol ( 2b ) with acetylacetone ( 1b ) yielded a bifuran, ethyl acetoacetate ( 1a ) led to a mixture of furan, bifuran, and salicylate derivatives. Besides, surprisingly, styryl‐substituted dihydrofurans were obtained from the reactions of 1,3‐dicarbonyl compounds and (3E)‐2,4‐diphenylbut‐3‐en‐2‐ol. The reaction mechanisms were proposed for the formation of the different products, considering intermediates in these reaction mixtures.     

Nitrosylation of Nitric‐Oxide‐Sensing Regulatory Proteins Containing [4Fe‐4S] Clusters Gives Rise to Multiple Iron–Nitrosyl Complexes

The reaction of protein‐bound iron–sulfur (Fe‐S) clusters with nitric oxide (NO) plays key roles in NO‐mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe‐S clusters has been hampered by a lack of information about the nature of the iron‐nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe‐4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe₂(NO)₄(Cys)₂]) and Roussin's Black Salt (RBS, [Fe₄(NO)₇S₃]. In the latter case, the absence of ³²S/³⁴S shifts in the Fe?S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates.     

Lewis Acid Catalyzed,Selective Cyclopropane‐Ring Opening in Ingol Diterpene Derivatives

Lewis acid mediated skeletal rearrangement of the ingol diterpenoids 1 and 4 via regio‐ and stereospecific cyclopropane‐ring opening afforded the four new compounds 2, 3, 5 , and 6 , named nivulianol A–D (Scheme 1). Their structures were established by means of IR, MS, and in‐depth NMR spectroscopic analyses. The rearranged congeners were tested for lipopolysaccharide (LPS)‐induced prostaglandin (PG) E₂ (cyclooxygenase‐2) inhibition. Thereby, nivulianol B (=(1S*,2E,4R*,5S*,7Z,9S*,11R,13S*,14S*)‐14‐acetoxy‐5‐methoxy‐3,9,13‐trimethyl‐6‐(1‐methylethenyl)‐10‐oxo‐15‐oxatricyclo[9.3.1.0^1,11]pentadeca‐2,7‐dien‐4‐yl (2Z)‐2‐methylbut‐2‐enoate; 3 ) was found to be significantly active, with an IC₅₀ value of 36.3 μg/ml.