Biosynthesis and 13C NMR assignment of cytovaricin, a neutral macrolide antibiotic

13C NMR analysis of 13C-labeled cytovaricin which was obtained by feeding sodium [1-13C]-, [2-13C]-, and [1,2-13C]acetates, [1-13C]- and [3-13C]propionates, [1-13C]isobutyrate and [methyl-13C]methionine to cultures of Streptomyces diastatochromogenes showed that the aglycone of cytovaricin is derived from nine acetate units, six propionate units and one isobutyrate unit and the methoxy group at C-3' of cymarose moiety is derived from the methionine-S-methyl group. The 13C NMR spectra of 13C-labeled cytovaricins which were obtained from feeding experiments allowed the complete assignment of the 13C NMR spectrum of cytovaricin.     

Biosynthetic origin of the carbon skeleton and oxygen atoms of the LL-F28249 alpha, a potent antiparasitic macrolide

The biosynthesis of LL-F28249 alpha in a culture of Streptomyces cyaneogriseus has been studied using 13C, 14C and 18O labeled precursors. A complete 13C NMR spectrum of F28249 alpha has been assigned. Incorporation studies using 13C labeled precursors indicate that the carbon skeleton of F28249 alpha is derived from seven acetate, six propionate and one 2-methylpropionate units. The origin of the oxygen atoms of F28249 alpha has been examined by feeding [1-13C,18O2]acetate, [1-13C,18O2]propionate, [2-13C]acetate/18O2 and 18O2 separately to the fermentation culture and analyzing the resulting labeled LL-F28249 alpha samples by 13C NMR, electron impact MS and chemical ionization MS. Out of a total of eight oxygen atoms in LL-F28249 alpha, four oxygen atoms are derived from acetate, three from propionate and one from molecular oxygen.     

Biosynthetic studies on a myxobacterial antibiotic,cystothiazole A: biosynthetic precursors of the carbon skeleton

Biosynthetic studies on cystothiazole A (1), a beta-methoxyacrylate-type antifungal compound from a myxobacterium, were performed by feeding the producing organism, Cystobacter fuscus, with stable-isotope-labeled compounds including [2-(13)C]acetate, [1,2-(13)C2]acetate, [1-(13)C]propionate, L-[1-(13)C]serine, L-[methyl-(13)C]methionine, and DL-valine-d8. The polyketide moiety of 1 was found to be derived from acetate and propionate, the bithiazole moiety from L-serine, the O-methyl groups from the S-methyl group of L-methionine, and the isopropyl moiety from L-valine, which should be the metabolic precursor of isobutyryl-CoA.     

Biosynthesis of quinolactacin A, a TNF production inhibitor

Quinolactacins, which inhibit tumor necrosis factor production, contain a quinolone skeleton conjugated with a y-lactam. The biosynthesis of quinolactacin was investigated by feeding experiments using 13C single-labeled precursors (sodium [1-13C]acetate, DL-[1-13C]-isoleucine, L-[methyl-13C]methionine, and sodium [1-13C]-anthranilate) and D-[U-13C]glucose.     

Biosynthesis of the avermectins by Streptomyces avermitilis. Incorporation of labeled precursors

The biosynthesis of the avermectins, a group of 16 membered macrolides with potent anthelmintic and insecticidal activity produced by Streptomyces avermitilis, was studied by supplying cultures with 14C and 13C precursors. [1-14C] and [2-14C]acetate and propionate were poor precursors of the avermectins and were instead rapidly oxidized to 14CO2. The S-methyl of methionine in contrast was incorporated extensively and equally into the three methoxyl groups of the avermectins. The carbon backbone of methionine was not a precursor of the avermectins. Feeding of [1-13C]glucose yielded avermectins labeled specifically in the C1' and C1" of the oleandrose moiety and in the aglycone moiety in carbons known to be derived from the methyl of acetate. Feeding [U-13C]glucose showed that the entire avermectin molecule is derived from glucose carbons.     

Urdamycins, new angucycline antibiotics from Streptomyces fradiae. IV. Biosynthetic studies of urdamycins A-D

The biogenetic origin of the angucycline antibiotics urdamycins A-D was studied by feeding experiments with isotope labeled precursors and by NMR analysis. Feeding experiments with [1-13C]acetate and [1,2-13C2]acetate show that the chromophores of urdamycins A and B and the angucycline 4-ring skeleton of the urdamycins C and D chromophores are formed from a single decapolyketide chain. The chromophores of the urdamycins C and D contain additional structural elements which derived from the amino acids tyrosine and tryptophan, respectively. The latter was shown by feeding deuterium-labeled tyrosine and 13C-labeled tryptophan derivatives. Feeding of [1-13C]glucose and of [U-13C3]glycerol proved that the C-glycosidic moiety and the three sugars (2 x L-rhodinose, 1 x D-olivose each) of the urdamycins arise from glucose. Experiments with 14C-labeled urdamycin A, obtained by biosynthesis from [14C]acetate, showed this compound to be a late precursor of the urdamycins C and D.     

Differentiating the biosynthesis of pseudomonic acids A and B

Pseudomonic acid A (1) has been the dominant commercial pseudomonate antibiotic produced by Pseudomonas fluorescens. In specific shaken flask conditions initial fermentation accumulation of 1 is followed by preferential accumulation of the 8-hydroxy derivative, pseudomonic acid B (2). Biosynthetic probing with a pulse of [1-14C] acetate or L-[methyl-14C] methionine at early, mid and late stages of the fermentation gave relative patterns of radioactivity in 1 and 2 that are inconsistent with an assumption that 2 arises by oxidation of 1, or that 1 is formed by reduction of 2. Since [methyl-14C] methionine only labels carbons in the 12-carbon part of the pseudomonate molecule that is thought to be an early biosynthetic moiety, the evidence from radiolabelling experiments implies that preferential early oxidation of this biosynthetic intermediate causes the pathway diversion to accumulate 2 instead of 1.     

Studies on the biosynthesis of epothilones: the biosynthetic origin of the carbon skeleton

The biosynthetic origin of the epothilone skeleton was studied by the incorporation of 13C and radioactively labeled precursors by Sorangium cellulosum So ce90. The carbon atoms are derived from acetate, propionate, the methyl group of S-adenosyl-methionine, and cysteine which also introduces the sulfur and nitrogen atoms. Epothilone biosynthesis starts with the formation of the thiazole part from acetate and cysteine. The incorporation of acetate or propionate units results in the formation of epothilones A and B, respectively. To introduce the epoxide function of epothilones A and B molecular oxygen is used.     

Ethyl-3H]RS-79948-197 alpha2-adrenoceptor autoradiography validation in alpha2-adrenoceptor knockout mice

[Ethyl-(3)H][8aR,12aS,13aS]-5,8,8a,9,10,11,12,12a,13,13a-decahydro-3-methoxy-12-(ethylsulfonyl)-6H-isoquino[2,1-g][1,6]naphthyridine ([ethyl-(3)H]RS-79948-197) was evaluated for alpha(2)-adrenoceptor autoradiography in brain sections from wild-type mice and alpha(2A)- and alpha(2ABC)-adrenoceptor knockout mice. Receptor numbers were 83% lower in cortex and 28% lower in caudate putamen of alpha(2A)-knockout mice than in wild-type mice. No specific binding was seen in alpha(2ABC)-knockout mice. [Ethyl-(3)H]RS-79948-197 saturation binding parameters were compared to those of [(3)H]2-(2,3-dihydro-2-methoxy-1,4-benzodioxan-2-yl)-4,5-dihydro-1H-imidazoline ([(3)H]RX821002) and [methyl-(3)H]17alpha-hydroxy-20alpha-yohimban-16beta-carboxylic acid methyl ester ([methyl-(3)H]rauwolscine). [Ethyl-(3)H-]RS-79948-197 detected a larger number of both alpha(2A)- and alpha(2B/C)-adrenoceptors than [(3)H]RX821002, while [methyl-(3)H]rauwolscine only underestimated the number of alpha(2A)-adrenoceptors. Oxymetazoline and prazosin competed for [ethyl-(3)H]RS-79948-197 binding with the expected rank order of affinities. Higher than necessary [ethyl-(3)H]RS-79948-197 concentrations resulted in a rapid increase in non-specific binding. Slow dissociation kinetics, high specific radioactivity and high alpha(2)-adrenoceptor affinity (slightly lower for the alpha(2A)-adrenoceptor than for the other subtypes) confer [ethyl-(3)H]RS-79948-197 distinct advantages compared to [(3)H]RX821002 for detection of alpha(2)-adrenoceptor subtypes in a mixed alpha(2)-adrenoceptor population.     

Evaluation of liver function with 13C-labelled amino acid using hepatectomized rat model

Using a rat model of hepatectomy, we investigated whether the severity of hepatopathy could be quantitatively measured from changes in expiratory 13CO2 levels after intravenous administration of L-[1-(13)C]phenylalanine, L-[1-(13)C]methionine or L-[1-(13)C]alanine. MATERIALS AND METHODS: Under nembutal anesthesia, 30 mg/kg L-[1-(13)C]phenylalanine, 40 mg/kg L-[1-(13)C]methionine or 20 mg/kg L-[1-(13)C]alanine was administered to rats through the femoral vein, and expiratory 13CO2 levels were measured for 15 min. Thirty percent, 70% or 90% hepatectomy was performed. In the control group, simple laparotomy was performed. RESULTS: The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]phenylalanine administration and liver weight/body weight was 0.883 (P < 0.001). The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]methionine administration and liver weight/body weight was 0.922 (P < 0.001). The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]alanine administration and liver weight/body weight was 0.902 (P < 0.0001). CONCLUSION: In the breath test with intravenously administered L-[1-(13)C]phenylalanine, L-[1-(13)C]methionine, or L-[1-(13)C]alanine, hepatopathy could be quantitatively evaluated by measuring expiratory 13CO2 levels over 15 min.     

Studies on new antifungal antibiotics, guanidylfungins A and B. II. Structure elucidation and biosynthesis

The structures of guanidylfungins A and B were elucidated from the physico-chemical properties of these compounds and the structures of the degradation products by ozonolysis and periodate oxidation. The guanidylfungins consist of a 36-membered polyhydroxyl lactone ring, a guanidine and a monoester of malonic acid. The labelling experiments with sodium [1-13C]acetate and sodium [1-13C]propionate revealed that twelve units of acetate and nine of propionate were incorporated into the molecule of guanidylfungin A.     

In vitro studies on L-771,688 (SNAP 6383), a new potent and selective alpha1A-adrenoceptor antagonist

L-771,688 (SNAP 6383, methyl(4S)-4-(3, 4-difluorophenyl)-6-[(methyloxy)methyl]-2-oxo-3-[(?3-[4-(2-pyridin yl)-1-piperidinyl]propyl?amino)carbonyl]-1,2,3, 4-tetrahydro-5-pyrimidine carboxylate) had high affinity (Ki less than or = 1 nM) for [3H]prazosin binding to cloned human, rat and dog alpha1A-adrenoceptors and high selectivity (>500-fold) over alpha1B and alpha1D-adrenoceptors. [3H]Prazosin / (+/-)-beta-[125I]-4-hydroxy-phenyl)-ethyl-aminomethylteralone ([125I]HEAT) binding studies in human and animal tissues known to contain alpha1A and non-alpha1A-adrenoceptors further demonstrated the potency and alpha1A-subtype selectivity of L-771,688. [3H]L-771,688 binding studies at the cloned human alpha1A-adrenoceptors and in rat tissues indicated that specific [3H]L-771,688 binding was saturable and of high affinity (Kd=43-90 pM) and represented binding to the pharmacologically relevant alpha1A-adrenoceptors. L-771,688 antagonized norepinephrine-induced inositol-phosphate responses in cloned human alpha1A-adrenoceptors, as well as phenylephrine or A-61603 (N-[5-4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7, 8-terahydro-naphthlen-1-yl] methanesulfonamide hydrobromide) induced contraction in isolated rat, dog and human prostate, human and monkey bladder neck and rat caudal artery with apparent Kb values of 0.02-0.28 nM. In contrast, the contraction of rat aorta induced by norepinephrine was resistant to L-771,688. These data indicate that L-771,688 is a highly selective alpha1A-adrenoceptor antagonist.     

Biosynthesis of the macrolide antibiotic patulolides by Penicillium urticae S11R59: identification of the origin of carbon atoms by 13C NMR spectroscopy

Patulolides are 12-membered macrolides produced by Penicillium urticae S11R59, and they are the simplest macrolide antibiotics. All carbon signals, including six methylene signals of patulolides A (1), B (2), and C (3), were completely assigned by use of the 13C two-dimensional INADEQUATE. The biosynthesis of patulolides was investigated with 13C labeled acetate. Feeding of [1-13C]acetate to a culture of P. urticae S11R59 gave patulolides A (1), B (2), C (3), each of which showed enrichment at carbons 1, 3, 5, 7, 9, and 11; enrichment at carbons 2, 4, 6, 8, 10, and 12 was observed upon feeding of [2-13C]acetate. These results showed that patulolides A (1), B (2), and C (3) are pure acetogenic hexaketides derived from six acetate units coupled in head-to-tail fashion.     

New antibiotics, carbazomycins A and B. III. Taxonomy and biosynthesis

The carbazomycin-producing microorganism, strain H 1051-MY 10, was determined to a strain of Streptoverticillium ehimense. Biosynthesis of carbazomycin B was studied using 14C-labeled and 13C-enriched precursors in combination with 13C NMR spectroscopy. The C-2 carbon of [2-13C]trytophan was shown to be involved at the C-3 carbon in carbazomycin B and both carbons of [1,2-13C]acetate at the C-1 and C-10 moiety of the antibiotic. [CH3-13C]Methionine was involved at the methoxyl group but not at the methyl group on the C-2 carbon of the antibiotic. Neither of the labeled carbons, [1-14C]tryptophan nor [2,3-13C]propionic acid, was detected in the antibiotic, and a progenitor of the C-2 and C-11 moiety of the antibiotic has not been determined.     

The squalestatins, novel inhibitors of squalene synthase produced by a species of Phoma. III. Biosynthesis.

The biosynthetic origin of the carbon and oxygen atoms of the novel fungal secondary metabolite 1 was studied. Incorporation studies with single and multiple labelled 13C precursors indicated that the major portion of the molecule was derived from two polyketide chains made up of acetate units. One of the chains had benzoic acid (which can be derived from phenylalanine) as a starter unit. The remaining carbons were derived from a four-carbon unit related to succinate and from methionine. Studies with [1-(13)C,18O2]acetate and 18O2 indicated that five of the oxygens, including both of the heterocyclic oxygens, were derived from atmospheric oxygen. The oxygens at the two ester carbonyls were derived from acetate.     

Use of carbon-13 in biosynthetic studies: origin of the malonyl coenzyme A incorporated into tetracycline by Streptomyces aureofaciens

The proton noise decoupled 13C nuclear magnetic resonance spectrum of tetracycline hydrochloride prepared from Streptomyces aureofaciens cultures supplemented with [1-13C]acetate and [2-13C]acetate showed enrichment of nine alternating ring carbons. In addition, a small enrichment of the carboxamide carbon by [1-13C]acetate was observed. The labelling patterns clearly demonstrated the polyketide origin of the tetracyclic nucleus. The 13C nuclear magnetic resonance spectrum of tetracycline hydrochloride derived from [1,2-13C]acetate showed all 18 ring carbons as doublets with coupling constants appropriate for the incorporation of nine intact two-carbon precursors, confirming that head-to-tail condensation of C2 units had occurred. Absence of bond scission within the C2 units and a low level of uncoupled 13C in the carboxamide substituent indicated that when the organism is supplemented with acetate, malonyl coenzyme A used for tetracycline biosynthesis is formed by direct carboxylation of acetyl coenzyme A.     

Biosynthesis of antibiotic 1233A (F-244) and preparation of [14C]1233A.

The biosynthesis of antibiotic 1233A (F-244) was studied by feeding 13C-labeled precursors to the producing organism, Scopulariopsis sp. F-244. 13C NMR spectroscopy established that 1233A is derived from 4 methionines and 7 acetates. Seven acetates are condensed to form a hexaketide and 4 methyl residues from methionine are introduced into the main skeleton. The beta-lactone is derived from the alpha-carboxylic acid of the hexaketide. Since methionine was efficiently incorporated into 1233A, radiolabeled 1233A was prepared biosynthetically by feeding [14C]methionine to the producer. As a result, [14C]1233A was obtained with high specific radioactivity (27.2 muCi/mumols).     

Milbemycins, a new family of macrolide antibiotics. Structure determination of milbemycins D, E, F, G, H, J and K

The milbemycins, a group of potent, broad-spectrum antiparasitic and pesticidal agents, are architecturally novel antibiotics of 16-membered macrocyclic lactone. Seven new milbemycin analogues designed as milbemycins D, E, F, G, H, J and K were isolated from the fermentation broth of the mutant strain of Streptomyces hygroscopicus subsp. aureolacrimosus. The structural determination of these new components was made mainly by comparing with mass spectra, and 1H and 13C NMR spectra of milbemycin alpha- and beta-series previously published from our laboratory. Milbemycins D, E, F, G and H have characteristically an isopropyl side chain at C-25 which differs from the known milbemycin family bearing methyl or ethyl group at C-25. Milbemycins J and K possess a ketone group at C-5 instead of a hydroxyl or methoxy group. Apart from X-ray crystallography, the R-configuration of the hydroxyl group at C-5 could be best explained both by application of CD allylic benzoate method to the n-N, N-dimethylaminobenzoate of milbemycin D and by comparison of the specific rotation of milbemycin D itself and its acetate with the epimeric isomers at C-5.     

Synthesis of milbemycins alpha9, alpha10, alpha11, alpha12, alpha14, alpha15, alpha20, alpha21, alpha22, alpha23, alpha26, alpha27, delta(2,3),delta(4,26)-milbemycins A3, A4 from milbemycins A3, A4, and their acaricidal activities

Chemical derivation methods to prepare 26-acyloxy and 26-hydroxymilbemycins, which had been reported as natural products, milbemycins alpha9, alpha10, alpha11, alpha12, alpha14, alpha15, alpha20, alpha21, alpha22, alpha23, alpha26, alpha27 from milbemycins A3, A4 were reported. Delta(2,3),delta(4,26)-milbemycins A3, A4, which had also been reported as natural products, were further prepared from milbemycins A3, A4. Their acaricidal activities were also assessed against the organophosphorus-sensitive two-spotted spider mite (Tetranychus urticae) on primary leaves of cowpea plants (Vigna sinesis Savi species) by spraying.     

新型H+/K+-ATP酶抑制剂泰妥拉唑的NMR测定分析

目的：测定泰妥拉唑的分子结构，并对化合物的^H NMR和^13C NMR谱峰信号进行归属分析。方法：采用一维、二维等核磁共振技术研究药物的分子结构。通过一维NOESY和二维远程^1H-^13C COSY技术测定分子中结构单元的连接位置。结果：通过对泰妥拉唑的结构测定，确证了该药物的分子结构。结论：目标化合物的NMR测定分析结果与泰妥拉唑的化学结构式相一致。