Dentin biomodification potential depends on polyphenol source

Although proanthocyanidins (PACs) modify dentin, the effectiveness of different PAC sources and the correlation with their specific chemical composition are still unknown. This study describes the chemical profiling of natural PAC-rich extracts from 7 plants using ultra high pressure/performance liquid chromatography (UHPLC) to determine the overall composition of these extracts and, in parallel, comprehensively evaluate their effect on dentin properties. The total polyphenol content of the extracts was determined (as gallic acid equivalents) using Folin-Ciocalteau assays. Dentin biomodification was assessed by the modulus of elasticity, mass change, and resistance to enzymatic biodegradation. Extracts with a high polyphenol and PAC content from Vitis vinifera, Theobroma cacao, Camellia sinensis, and Pinus massoniana induced a significant increase in modulus of elasticity and mass. The UHPLC analysis showed the presence of multiple types of polyphenols, ranging from simple phenolic acids to oligomeric PACs and highly condensed tannins. Protective effect against enzymatic degradation was observed for all experimental groups; however, statistically significant differences were observed between plant extracts. The findings provide clear evidence that the dentin bioactivities of PACs are source dependent, resulting from a combination of concentration and specific chemical constitution of the complex PAC mixtures.

Enterococcus faecalis multi-drug resistance transporters: application for antibiotic discovery

Using bioinformatics approaches, 34 potential multidrug resistance (MDR) transporter sequences representing 4 different transporter families were identified in the unannotated Enterococcus faecalis database (TIGR). A functional genomics campaign generating single-gene insertional disruptions revealed several genes whose absence confers significant hypersensitivities to known antimicrobials. We constructed specific strains, disrupted in a variety of previously unpublished, putative MDR transporter genes, as tools to improve the success of whole-cell antimicrobial screening and discovery. Each of the potential transporters was inactivated at the gene level and then phenotypically characterized, both with single disruption mutants and with 2-gene mutants built upon a delta norA deleted strain background.

Production of brominated tiacumicin derivatives

Several novel tiacumicin derivatives containing bromine have been produced by the addition of inorganic bromine to the fermentation both of Dactylosporangium aurantiacum subsp, hamdenensis. Structures were elucidated employing mass spectrometry and NMR spectroscopy. Antibacterial activity of the bromotiacumicins is comparable to that of the parent compounds.

Novel triterpene sulfates from Fusarium compactum using a rhinovirus 3C protease inhibitor screen

Two novel triterpene sulfates have been isolated from Fusarium compactum by bioactivity-directed fractionation using an assay which measures the inhibition of proteolytic activity of rhinovirus 3C protease on a fluorogenic peptide substrate. The compounds were purified by countercurrent and reverse phase chromatographies. NMR, MS, UV and IR studies revealed two triterpene sulfates, uncommon metabolites of terrestrial fungi.

A method for the selective isolation of Myxococcus directly from soil

A new method is described for the selective isolation of species of Myxococcus directly from soil by dilution plating. The method involves suppression of competing microorganisms with antibiotics combined with air drying and wet heat treatment of soils. Fungi were eliminated by supplementing the plating medium with cycloheximide and nystatin. Non-sporulating bacteria were controlled by air drying soils and then heating aqueous soil dilutions for 10 min at 56 degrees C. The predominant sporulating bacteria in soil, Streptomyces and Bacillus, were suppressed by adding either tiacumicin B, ristocetin or vancomycin to the medium. Swarming of Myxococcus colonies was controlled with a casein digest-yeast extract plating medium (CY-C10 agar). Ultrasound treatment of soil suspensions gave the highest number of Myxococcus colonies in the soils studied, but these cultures could be recovered without ultrasound. Strains of Myxococcus fulvus, M. xanthus, M. coralloides, M. stipitatus and M. virescens were isolated from soil using this technique. Soils examined yielded one or two Myxococcus species per sample.

Dibefurin, a novel fungal metabolite inhibiting calcineurin phosphatase activity

The novel calcineurin inhibitor, dibefurin, has been isolated from the fungal culture AB 1650I-759. The isolation was bioactivity-directed fractionation using an assay which measures the phosphatase activity of calcineurin. The compound was purified by countercurrent, reverse phase and gel filtration chromatographies. Several studies, including crystallographic, NMR and MS, revealed that dibefurin is a novel dimeric compound of a unique structural type.

Fusacandins A and B; novel antifungal antibiotics of the papulacandin class from Fusarium sambucinum. II. Isolation and structural elucidation

Two novel antifungal compounds of the papulacandin class, named fusacandins A and B, have been isolated from Fusarium sambucinum. Each compound contains two units of galactose and one of glucose, the latter connected as a C-glycoside to an aromatic moiety. Fusacandin A is esterified at two sites with long-chain, unsaturated fatty acids and fusacandin B at only one site. The structures of the fusacandins were elucidated through analysis of mass spectral and 1-D and 2-D homonuclear and heteronuclear NMR data.

Macquarimicins, microbial metabolites from Micromonospora. II. Isolation and structural elucidation

A novel series of carbocyclic compounds has been isolated from two related Micromonospora cultures. The C-19 and C-22 macquarimicins represent different end products on a similar biosynthetic scheme. 1-D and 2-D homonuclear and heteronuclear NMR experiments allowed assignment of the basic structures of the macquarimicins. An X-ray structure of macquarimicin B suggested the stereochemistry for the series which was not discernible from spectroscopic data alone.

Macquarimicins, microbial metabolites from Micromonospora. I. Discovery, taxonomy, fermentation and biological properties

A novel series of microbial metabolites were discovered in fermentation broths of two soil isolates. Both cultures were identified as strains of Micromonospora chalcea. Production of the metabolites, named macquarimicins, was monitored by an HPLC assay. A seven-day fermentation yielded 27 mg/liter of macquarimicin A. With MICs of 50 to 100 micrograms/ml, macquarimicin A has only very low activity against strains of Bacteroides and other anaerobes. Macquarimicin B has inhibitory activity against the leukemia cell line P-388.

Dorrigocins: novel antifungal antibiotics that change the morphology of ras-transformed NIH/3T3 cells to that of normal cells. II. Isolation and elucidation of structures

Two novel antifungal antibiotics, named dorrigocin A and B have been isolated from the fermentation broth and mycelium of Streptomyces platensis subsp. rosaceus. These closely related compounds were separated from one another by countercurrent chromatography on an Ito coil planet centrifuge. The structures of the dorrigocins were determined by NMR and IR spectroscopy and mass spectrometry. Each is a putative propionate-acetate derived straight chain fatty acid terminating in cycloheximide. The dorrigocins differ from one another only in their oxidation pattern.

Dorrigocins: novel antifungal antibiotics that change the morphology of ras-transformed NIH/3T3 cells to that of normal cells. III. Biological properties and mechanism of action

The dorrigocins are unique glutarimide antibiotics which were found to reverse the morphology of ras-transformed NIH/3T3 cells from a transformed phenotype to a normal one. The compounds also inhibited the release of yeast mating pheromone, a-factor. The activity of these compounds was not dependent on inhibition of prenylation or protein synthesis. Dorrigocin A was instead found to inhibit the carboxyl methylation in K-ras transformed cells.

Aselacins, novel compounds that inhibit binding of endothelin to its receptor. I. The producing organism, fermentation and biological activity

A radioligand test to detect inhibitors of endothelin-1 binding to its receptors in bovine atrial and porcine cerebral membranes was used to screen fungal metabolites from stationary fermentations. Inhibitory activity, observed in culture extracts of two Acremonium species, led to the discovery of aselacins A, B and C. Aselacin A inhibits binding to both membrane fractions with IC50s of approximately 20 micrograms/ml.

Aselacins, novel compounds that inhibit binding of endothelin to its receptor. II. Isolation and elucidation of structures

Three novel compounds, named the aselacins, which inhibit the binding of endothelin to its receptor have been isolated from two related Acremonium species of fungi grown in stationary culture. These compounds are cyclic pentapeptolides with a ring formed by cyclo[Gly-D-Ser-D-Trp-beta-Ala-L-Thr] and an additional exocyclic D-Gln to which is attached a functionalized long chain fatty acid. The aselacins differ in the functionalization of this acid. The structures of the aselacins were determined by amino acid analysis, mass spectrometry and evaluation of 1-D and 2-D homonuclear and heteronuclear 1H, 13C and 15N NMR spectra in protic and aprotic solvents. The stereochemistry of the amino acids present was elucidated by chiral HPLC of hydrolyzed compound.

MLR-52, (4'-demethylamino-4',5'-dihydroxystaurosporine), a new inhibitor of protein kinase C with immunosuppressive activity

In the course of screening with the mixed lymphocyte reaction, a new inhibitor of protein kinase C with immunosuppressive activity was isolated from the fermentation broth and mycelia of Streptomyces sp. AB 1869R-359. Although certain similarities exist, this strain is morphologically and physiologically distinct from other reported producers of staurosporine-related compounds. We have found that this strain produces relatively high levels of staurosporine and the new minor compound MLR-52, which possesses the indolo[2,3-a]carbazole chromophore of staurosporine, but differs in the substitution pattern of the sugar moiety. Their structures have been elucidated by mass and NMR spectra. MLR-52 has been shown to inhibit the enzymatic activity of protein kinase C and the murine mixed lymphocyte reaction.

An erythromycin analog produced by reprogramming of polyketide synthesis

The polyketide-derived macrolactone of the antibiotic erythromycin is made through successive condensation and processing of seven three-carbon units. The fourth cycle involves complete processing of the newly formed beta-keto group (beta-keto reduction, dehydration, and enoyl reduction) to yield the methylene that will appear at C-7 of the lactone ring. Synthesis of this molecule in Saccharopolyspora erythraea is determined by the three large eryA genes, organized in six modules, each governing one condensation cycle. Two amino acid substitutions were introduced in the putative NAD(P)H binding motif in the proposed enoyl reductase domain encoded by eryAII. The metabolite produced by the resulting strain was identified as delta 6,7-anhydroerythromycin C resulting from failure of enoyl reduction during the fourth cycle of synthesis of the macrolactone. This result demonstrates the involvement of at least the enoyl reductase from the fourth module in the fourth cycle and indicates that a virtually complete macrolide can be produced through reprogramming of polyketide synthesis.

5-N-acetylardeemin, a novel heterocyclic compound which reverses multiple drug resistance in tumor cells. II. Isolation and elucidation of the structure of 5-N-acetylardeemin and two congeners

A family of novel compounds has been detected and isolated following an assay for the attenuation of multiple drug resistance in tumor cells from the fermentation broth and mycelia of a strain of Aspergillus fischeri which we have designated var. brasiliensis. The structures of three components were determined employing 1-D and 2-D homonuclear and heteronuclear NMR spectroscopy and mass spectrometry. The structure of 5-N-acetylardeemin was confirmed by single crystal X-ray diffraction. These compounds are most closely structurally related to asperlicin E1).

5-N-acetylardeemin, a novel heterocyclic compound which reverses multiple drug resistance in tumor cells. I. Taxonomy and fermentation of the producing organism and biological activity

The ardeemins are a new family of secondary metabolites produced by submerged fermentation of a fungus which was isolated from a soil sample collected in Brazil. Based on taxonomic studies, the producing culture was identified as Aspergillus fischeri var. brasiliensis strain AB 1826M-35. 5-N-Acetylardeemin potentiated the cytotoxicity of the anticancer agent vinblastine in multidrug resistant human tumor cells.

Calbistrins, novel antifungal agents produced by Penicillium restrictum. II. Isolation and elucidation of structure

The novel antifungal agents, calbistrins A, B, C and D have been isolated from a strain of Penicillium restrictum (AB 1875C-28). The four congeners were separated by bioactivity directed fractionation using countercurrent chromatography and preparative-HPLC. NMR studies revealed that the calbistrins each contain a carboxylic acid conjugated tetraene attached through an aliphatic ester linkage to a hexahydronaphthalene system.

Biosynthesis of the erythromycin macrolactone and a rational approach for producing hybrid macrolides

The three eryA genes involved in the formation of the polyketide portion of the macrolide antibiotic erythromycin in Saccharopolyspora erythraea, appear to be organized in a single transcriptional unit on the basis of the results of gene disruption experiments. An insertion sequence-like element of lower G + C content separates eryAI from eryAII. The organization of the enzymatic domains present in the eryA-encoded multifunctional polypeptides, determined by computer-assisted analysis, is presented. This has enabled the determination of a putative dehydratase domain. A rational approach for producing novel macrolides by introducing selected changes in polyketide synthase genes is outlined. The isolation of a lactone intermediate resulting from an early synthesis step in macrolactone formation is also presented.

Dunaimycins, a new complex of spiroketal 24-membered macrolides with immunosuppressive activity. II. Isolation and elucidation of structures

A novel complex of antifungal and immunosuppressant compounds has been isolated from the fermentation broth and mycelia of two strains of Streptomyces diastatochromogenes. The structures of eight related components were determined employing 1D and 2D homonuclear and the heteronuclear NMR spectroscopy and mass spectrometry. These structures represent the first reported spiroketal 24-membered macrolide natural products related to the common 26-membered oligomycins.

Modular organization of genes required for complex polyketide biosynthesis

In Saccharopolyspora erythraea, the genes that govern synthesis of the polyketide portion of the macrolide antibiotic erythromycin are organized in six repeated units that encode fatty acid synthase (FAS)-like activities. Each repeated unit is designated a module, and two modules are contained in a single open reading frame. A model for the synthesis of this complex polyketide is proposed, where each module encodes a functional synthase unit and each synthase unit participates specifically in one of the six FAS-like elongation steps required for formation of the polyketide. In addition, genetic organization and biochemical order of events appear to be colinear. Evidence for the model is provided by construction of a selected mutant and by isolation of a polyketide of predicted structure.

An erythromycin derivative produced by targeted gene disruption in Saccharopolyspora erythraea

Derivatives of erythromycin with modifications at their C-6 position are generally sought for their increased stability at acid pH, which in turn may confer improved pharmacological properties. A recombinant mutant of the erythromycin-producing bacterium, Saccharopolyspora erythraea, produced an erythromycin derivative, 6-deoxyerythromycin A, that could not be obtained readily by chemical synthesis. This product resulted from targeted disruption of the gene, designated eryF (systematic nomenclature, CYP107), that apparently codes for the cytochrome P450, 6-deoxyerythronolide B (DEB) hydroxylase, which converts DEB to erythronolide B (EB). Enzymes normally acting on EB can process the alternative substrate DEB to form the biologically active erythromycin derivative lacking the C-6 hydroxyl group.

Altromycins, novel pluramycin-like antibiotics. II. Isolation and elucidation of structure

A novel complex of Gram-positive antibiotics was produced from the fermentation of an actinomycete culture AB 1246E-26. The antibiotics were recovered from the whole fermentation broth by extraction with organic solvent and isolated using counter-current chromatography. UV and IR data place these compounds in the anthraquinone-derived class of antibiotics. Mass spectral and NMR data indicate a new complex of compounds related to, but distinctly different from the pluramycin type antibiotics.

Altromycins, novel pluramycin-like antibiotics. I. Taxonomy of the producing organism, fermentation and antibacterial activity

The altromycins are novel anthraquinone-derived antibiotics related to the pluramycins. They are produced by an actinomycete, AB 1246E-26, which was isolated from a South African bushveld soil. The altromycins have Gram-positive antibacterial activity with MICs of 0.2 to 3.12 micrograms/ml against Streptococci and Staphylococci.

Pacidamycins, a novel series of antibiotics with anti-Pseudomonas aeruginosa activity. II. Isolation and structural elucidation

A novel class of antibiotics was isolated from cultures of Streptomyces coeruleorubidus strain AB 1183F-64. The antimicrobial activity of the pacidamycins is selective against Pseudomonas aeruginosa. The various congeners are nucleoside peptides which differ in the terminal amino acid residues. The structures were determined using MS-MS and 2D NMR techniques.

Coumamidines, new broad spectrum antibiotics of the cinodine type. II. Isolation and structural elucidation

Two novel, isomeric compounds, coumamidines gamma 1 and gamma 2, were isolated from fermentations of an actinomycete. The structures were elucidated spectroscopically using 2D NMR correlation experiments and mass spectral data. The coumamidines were found to be close structural relatives of the cinodines (LL-BM123 gamma 1 and gamma 2).

Phenelfamycins, a novel complex of elfamycin-type antibiotics. II. Isolation and structure determination

A novel complex of elfamycin-type antibiotics has been isolated from submerged fermentation of either Streptomyces violaceoniger AB 999F-80 or Streptomyces violaceoniger AB 1047T-33. Antibiotics were extracted from the fermentation broth with ethyl acetate and from the mycelia with acetone. Purification of individual components was achieved by a combination of solvent partitions, Sephadex LH-20 exclusion, C18 bonded-phase silica gel adsorption, diol partition and liquid-liquid countercurrent chromatographies. Seven closely related components were separated and assigned structures 4, 11, 12, 13, 14, and 16 to phenelfamycins A to F respectively and structure 17 to unphenelfamycin. These structures were elucidated employing a variety of spectroscopic techniques, including extensive use of 1D and 2D NMR spectroscopy.

Tirandalydigin, a novel tetramic acid of the tirandamycin-streptolydigin type. II. Isolation and structural characterization

Tirandalydigin a structurally unique hybrid of the tirandamycin-streptolydigin families of tetramic acid antibiotics has been isolated from the fermentation beers of Streptomyces sp. AB-1006A-9. The structure of this anti-anaerobic antibiotic has been characterized based upon NMR, UV and mass spectrometric data.

Coloradocin, an antibiotic from a new Actinoplanes. II. Identity with luminamicin and elucidation of structure

Coloradocin was isolated from a fermentation broth by adsorption onto Amberlite XAD-2. The activity was eluted in MeOH and purified by gel filtration on Shephadex LH-20, followed by liquid-liquid chromatography on diol-bonded silica gel. The last two steps in the purification of this antibiotic included reverse-phase chromatography on C18-bonded silica gel and countercurrent chromatography on an Ito Coil Planet Centrifuge to give material of 90% purity. Analytically pure material was obtained by preparative HPLC. As a result of extensive homo and heteronuclear two-dimensional NMR studies, a structure was proposed for coloradocin. The structure consists of a decalin ring system fused to a 10-membered macrolactone which in turn is fused to a 14-membered macrolactone possessing an enol ether in conjugation with an unsaturated cyclic anhydride functionality. Coloradocin is related to a small class of antibiotics which include nodusmicin and nargenicin and was shown to be identical to luminamicin for which no structure has been reported.

New antibiotics from genetically engineered actinomycetes. I. 2-Norerythromycins, isolation and structural determinations

Novel macrolide antibiotics have been isolated from a genetically manipulated actinomycete. The major components produced have been isolated and identified as 2-norerythromycins A, B, C and D by mass spectrometry and extensive 1D and 2D NMR experiments.

Tiacumicins, a novel complex of 18-membered macrolides. II. Isolation and structure determination

A novel complex of Gram-positive antibiotics has been isolated from the fermentation broth and mycelium of Dactylosporangium aurantiacum subsp. hamdenesis subsp. nov. The structures of these six compounds were deduced employing UV, MS, IR, and extensive 1D and 2D homonuclear and heteronuclear NMR experiments. Each component contained a highly unsaturated 18-membered macrolide ring. Components differed from one another by minor structural variations in the macrolide ring and by the number and esterification pattern of glycosidically bound sugars.

Arizonins, a new complex of antibiotics related to kalafungin. II. Isolation and characterization

A new complex of anti-Gram-positive antibiotics was produced by the fermentation of Actinoplanes arizonaensis sp. nov. The antibiotics were recovered from the fermentation broth with Amberlite XAD-7 resin and from the mycelium by acetone lysis. UV, IR, MS and NMR spectral studies characterized these compounds as kalafungin-type antibiotics. They differ from other known members by an unusual oxidation pattern on the aromatic ring. They vary from one another by the degree and position of O-methylation on the aromatic ring and in the aliphatic portion of the molecules. The structure of one component was confirmed by X-ray diffraction analysis.

Abbeymycin, a new anthramycin-type antibiotic produced by a streptomycete

A new antibiotic, abbeymycin, has been isolated from Streptomyces sp. AB-999F-52. The structure of abbeymycin was assigned on the basis of NMR, mass spectrometric and UV spectral data. Abbeymycin has weak activity against a limited number of anaerobic bacteria.

Benzanthrins A and B, a new class of quinone antibiotics. II. Isolation, elucidation of structure and potential antitumor activity

The benzanthrins, which were produced by Nocardia lurida, were extracted from the fermentation broth with CH2Cl2. Subsequent purification on Sephadex LH-20 and diolbonded silica gel, followed by countercurrent chromatography, afforded analytically pure benzanthrins A and B. FAB-MS revealed that benzanthrins A and B were isomeric. It was demonstrated through degradative and spectroscopic studies that the benzanthrins were di-glycosides of a trihydroxy benz[a]anthraquinone chromophore where one of the sugars was linked through carbon and the other through oxygen. Benzanthrins A and B differed in the stereochemistry of the O-glycosidic sugar. Both compounds inhibited the growth of Gram-positive bacteria and 9KB, 9PS and 9ASK tumor cells in tissue culture.

Spenolimycin, a new spectinomycin-type antibiotic. II. Isolation and structure determination

A new water-soluble, basic antibiotic has been isolated from the fermentation beers of Streptomyces gilvospiralis sp. nov. The structure of the antibiotic has been deduced from spectral studies and confirmed by chemical degradation to spectinomycin. This structure, 3'-O-methylspectinomycin-3',4'-enol ether has led to the name spenolimycin.

Lysinomicin, a new aminoglycoside antibiotic. II. Structure and stereochemistry

The structure of lysinomicin, a new aminocyclitol antibiotic, was established as 3-epi-2'-N-(L-beta-lysyl)-4',5'-didehydro-6'-de-C-methylfortimi cin B (1) on the basis of spectral evidence and chemical degradation of the antibiotic. In the course of the degradation of 1, three additional compounds with interesting biological properties were obtained: 3-epi-2'-N-(L-beta-lysyl)-6'-de-C-methylfortimicin B (4), 3-epi-4',5'-didehydro-6'-de-C-methylfortimicin B (6) and 3-epi-6'-de-C-methylfortimicin B (7).

Modification of seldomycin factor 5 at C-3'

Attempted removal of the 3'-hydroxyl group of seldomycin factor 5 via displacement of a sulfonate ester has led to 3'-epi-seldomycin factor 5. Removal of the hydroxyl group has been effected by the Barton procedure. The antibacterial activity of 3'-epi- and 3'-deoxyseldomycin factor 5 against various aminoglycoside-resistant strains is discussed.

The structures of the m-chloroperbenzoic acid oxidation products of 8,9-anhydroerythromycins A- and B-6,9-hemiacetal and of (8S)-8-hydroxyerythromycin B

13C-NMR studies have confirmed the structures of (8S)-8-hydroxyerythromycins A- and B-6,9;9,11-acetal proposed by KROWICKI and ZAMOJSKI2,3) for the products of the m-chloroperbenzoic acid oxidation of 8,9-anhydroerythromycins A- and B-6,9-hemiacetal. The preparations of (8S)-8-methylthiomethoxy- and (8S)-8-methoxyerythromycin B-6,9;9,11-acetals are described. The latter are stable in aqueous acetic acid under conditions which convert (8S)-8-hydroxyerythromycin B-6,9;9,11-acetal into (8S)-8-hydroxyerythromycin B.

A new aminoglycoside antibiotic complex--the seldomycins. III. The structures of seldomycin factors 1 and 2+

The structures of seldomycin factors 1 and 2 have been determined by consideration of chemical degradation and spectral properties. Factor 1, also known as XK-88-1, is shown to be 6-O-(2-amino-2-deoxy-alpha-D-xylopyranosyl) paromamine (1) and factor 2, also known as XK-88-2, is shown to be 4'-deoxy-neamine (2). Mass spectral evidence has been obtained that suggests the most probable structure for seldomycin factor 3, also known as XK-88-3, is 6'-amino-6'-deoxyseldomycin factor 1 (12).

The absolute stereochemistry of piptoside and dihydropiptosidin

The absolute stereochemistry of piptoside and dihydropiptosidin has been determined at C5, C6 and C7 by comparison of dihydropiptosidin and leucodrin by means of molecular-rotation changes and p.m.r. spectroscopy, and by application of Horeau's method. Examination of p.m.r. parameters of some piptoside derivatives allows a tentative formulation at C4 and, together with previous results, allows the absolute stereochemistry of piptoside to be written as 2S,3S,4S,5S,6R,7S.

The nature of some derivatives of leucodrin

The structures of O-isopropylideneleucodrin aryl methyl ether and leucodrin nor-aldehyde have been revised on the basis of spectroscopic studies of these compounds and their acetyl derivatives.

Nitration and bromination reactions of galbulin

Nitration of the 1-phenyltetralin lignan, galbulin, occurs initially with dealkylative nitration at C 9 and cleavage of the C 1-C 9 bond. Subsequent reaction of the carbonium ion formed at C 1 with nitrate ion, and the degree of nitration of the aromatic rings, determine the final products. In contrast, bromination is not dealkylative and occurs initially at C 6? in ring c and subsequently at C 5 (ring A). Bromination in acetic acid in the presence of pyridine is accompanied by an unusual aromatic reaction, acetoxylation at C 8.