Biosynthesis of the cytochalasans. Part III. C-NMR. of cytochalasin B (phomin) and cytochalasin D. Incorporation of [1-13C]- and [2-13C]-sodium acetate

Sequential single frequency decoupling and partially relaxed Fourier transform (PRFT) are used to assign the natural abundance ¹³C-NMR. spectra of cytochalasin B (phomin) ( 1 ) and cytochalasin D ( 2 ). Cultures of Phoma spec. S 298 were fed [2-¹³C]-sodium acetate, and the distribution of this precursor in cytochalasin B (phomin) ( 1 ) was determined by ¹³C-NMR. spectroscopy. Likewise, the labelling patterns in cytochalasin D (zygosporin A) ( 2 ) from Zygos-posium masonii could be identified after incorporation of [2-¹³C]-sodium acetate and [l-¹³C]-sodium acetate. The results confirm previous proposals for the biogenesis of the cytochalasans from phenylalanine, methionine, and a C₁₈, or C₁₆, polyketide part.     

Biosynthesis of the antibiotic verrucarin E use of [1-13C]-, [2-13C]-, [1,2-13C]- and [2-13C, 2-2H3]-acetates. Verrucarins and roridins, 37th communication [1]

The origin of the carbon skeleton of verrucarin E (1) from acetate as precursor is confirmed. Incorporation studies with [1,2-¹³C]-acetate have demonstrated that two acetoacetate units couple together as shown in pattern A (Scheme 2) and not as in B . Analysis of the deuterium distribution in both verrucarin E (1) isolated after the incorporation of [2-¹³C,2-²H₃]-acetate and in sodium acetate obtained after Kuhn-Roth oxidation of the metabolite demonstrated that C(7) is derived from the starter unit of one of the acetoacetate moieties. The deuterium exchange in verrucarin E (1) occurring during fermentation was investigated.     

Design,synthesis and structure determination of new inherently chiral para-bromoalkoxycalix[4]arenes

The preparative method for the synthesis of inherently chiral para-bromoalkoxycalix[4]arenes based on para-bromination, stepwise regioselective debenzoylation and the following alkylation of the readily available 25-propoxy-26,27-dibenzoyloxycalix[4]arene with propyl bromide or (R)-N-(1-phenylethyl)bromoacetamide has been developed. Three types of the inherently chiral calix[4]arenes in cone or partial cone conformations with asymmetrical (_AHHH^HBHH, _AAHH^HBHH, _AHBH^HCHH) substitution of both upper and lower rims have been obtained in racemic, diastereomerically pure or enantiomerically pure forms. Their structure and the absolute configuration have been determined by NMR and X-ray.     

Synthesis of [5'-13C]ribonucleosides and 2'-deoxy[5'-13C]ribonucleosides

The present efficient synthesis of [5'-13C]ribonucleosides and 2'-deoxy[5'-13C]ribonucleosides is characterized by the synthesis of the D-[5-13C]ribose derivative as an intermediate via the Wittig reaction of 4-aldehydo-D-erythrose dialkyl acetals with Ph3P13CH3I-BuLi to introduce the 13C label at the 5-position of a pentose. This was followed by the highly diastereoselective osmium dihydroxylation for the preparation of 2,3-di-O-benzyl-D-[5-13C]ribose dialkyl acetal and the cyclization from D-[5-13C]ribose dialkyl acetal derivatives to the alkyl D-[5-13C]ribofuranoside derivative by the use of LiBF(4). The obtained D-[5-13C]ribose derivative was converted into [5'-13C]ribonucleosides and subsequently into the corresponding 2'-deoxynucleosides.     

Synthesis and 13C, 15N NMR study of a new functionalized pyrido[2,3-b]indole derivative

New functionalized α-carbolinones especially the 4-hydroxy-3-nitro-1H,9H-pyrido[2,3-b]indol-2-one were synthesized in a good yield, three-step reaction. A complete ¹³C, ¹⁵N nmr study of this carbolinone and precursors is presented.     

Isolation and structure determination of the cembranoid eunicin from a new genus of octocoral, Pseudoplexaura

The known cembranoid diterpene eunicin (1) was isolated from a new genus of octocoral, Pseudoplexaura, collected in the Caribbean. The complete assignment of the 13C and 1H NMR spectra, including differentiation of pro-R and pro-S hydrogens and elucidation of all J values, was accomplished with the aid of TOCSY, HSQC, and HMBC data, and a consideration of three low-energy conformations using SYBYL.     

Fused s-triazino heterocycles. XV. 13H-4,6,7,13a,13c-pentaazabenzo[hi]chrysene, 13H-4,7,13a,13c-tetraazabenzo[hi]chrysene,and 7H-3,7,10,10b-tetraazacyclohepta[de]naphthalene,three new ring systems

The reaction of N-cyano-N′-(6-amino-2-pyridyl)acetamidine ( 5a ) and homophthalic anhydride followed by ring closure of the 2-[2-(carboxymethyl)phenyl]-5-methyl-1,3,4,6,9b-pentaazaphenalene intermediate ( 4a ) gave 5-methyl-13-oxo-13H-4,6,7,13a,13c-pentaazabenzo[hi]chrysene ( 8a ). An analogous series starting with 3-N-(6-amino-2-pyridyl)amino-2-cyano-2-butenenitrile ( 5b ) in place of 5a gave in two steps 5-methyl-13-oxo-13-H-4,7,13a,13c-tetraazabenzo[hi]chrysene-6-carbonitrile ( 8b ). Elemental analysis, ir and pmr spectra of 8a , 8b and several new model compounds aided in confirming the structures of 8a and 8b. The synthesis of one of these model compounds for 5b and phenylacetic anhydride led surprisingly to 2-methyl-9-phenyl-7H-3,7,-10,10b-tetraazacyclohepta[de]naphthalene ( 10 ) in addition to the expected 2-benzyl-4-cyano-5-methyl-1,3,-6,9b-tetraazaphenalene ( 7b ).     

Synthesis,structure and reactivity of a macrocyclic imine: aza-[13]-macrodiolides

The in situ synthesis and subsequent reactions of macrocylic imine 2 are reported. The imine was trapped with cyanotrimethylsilane to give α-amino nitrile aza-[13]-macrodiolides in a 1:1 ratio of diastereomers. A crystal structure of the syn α-cyano nitrile diastereomer, 7a, provided insights into the lack of selectivity in reactions of 2 relative to macrocyclic alkene 1. Reactions to functionalize the syn diastereomer 7a are also reported.     

[13C]NMR study of naphthoflavones

The [¹³C]NMR spectra of α-,β- and γ-naphthoflavones were assigned at 25.2 MHz resorting to models such as the unsubstituted flavone and appropriate substituted acetylmethoxynapthalenes. Supporting evidence for the assignments was provided by gated decoupled spectra and all the chemical shifts in the 11 compounds studied gave a self-consistent data set.     

A new [4]carceplex, and a crystal structure and dynamic combinatorial chemistry of a [5]carceplex

A new [4]carceplex (2·guest) is reported. It is composed of two cavitands linked by four disulfide bonds. It forms twistomers, which interconvert on a millisecond timescale. The energy barrier for interconversion of twistomers is guest-dependent. Formation of [4]carceplex 2·guest is template dependent. The selectivity in templates is flat relative to most previous related template work. Larger kin [5]carceplex 1·guests were reinvestigated. A crystal structure confirms the twist between the hemispherical cavitands. Use of a redox buffer allowed dynamic combinatorial chemistry to be performed between pairs of templates.     

1H and 13C NMR structure determination of a new stereoisomer of isoreserpiline pseudoindoxyl from Rauvolfia grandiflora

An NMR study of a new stereoisomer of isoreserpiline pseudoindoxyl alkaloid is described. The complete ¹H and ¹³C NMR assignments of the compound were carried out using COSY, HMQC and HMBC. Stereochemistry at carbons C‐2, C‐3, C‐15, C‐20 and C‐19 was established using values of ¹H chemical shifts, coupling constants and NOESY experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

The mass spectra of [17-13C]phyllocladene and [3-13C]methylenecholestane—III

The mass spectra of [17-¹³C]phyllocladene and [3-¹³C]methylenecholestane have been examined. It is shown that there are some rearrangements at 70 e V as in the case of [17-¹³C]kaurene. However, no extensive randomization is evident at the molecular ion level. The results are interesting because very little is known about ¹³C randomization in polycyclic aliphatic hydrocarbons. The percentage retention of label was calculated for each ion.     

Isolation and structure determination of a new sesquiterpene lactone from Nauplius aquaticus

The aerial part of Nauplius aquaticus afforded a new sesquiterpene lactone with a humulanolide skeleton, 6,7,9,10-tetrahydroasteriscunolide (1), in addition to the known asteriscunolides A (2) and D (3). Their structures were established principally by two-dimensional NMR spectroscopy.     

13C tracer recovery in human stools after digestion of a fat-rich meal labelled with [1,1,1-13C3]tripalmitin and [1,1,1-13C3]triolein

Lipid metabolism studies focus mainly on oxidation and storage but rarely on faecal elimination, which is needed to assess total lipid distribution during the postprandial period. The purpose of the present work was to set up and validate the analysis of lipid tracers in stools, with an aim of later using this methodology in studies of postprandial lipid tracer metabolism. Eight subjects received a mixture of [1,1,1-(13)C3]tripalmitin and [1,1,1-(13)C3]triolein with a fat-rich meal. The nature and amounts of (13)C lipids excreted in stools during 3 days post-dose were determined by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis of fatty acid methyl esters (FAMEs) from total fatty acid (TFA), free fatty acid (FFA) and triacylglycerol (TAG) fractions. The results were expressed as the Cumulative Tracer Recovery of the administered dose (CTR%). The quantities and labelling of FAMEs were higher in FFA than in TAG, indicating that label loss was not due to a lack of digestive lipase activity. The labelling was higher for C16:0 than for C18:1. The CTRs were 7.03 ± 0.77% and 6.87 ± 0.91%, respectively, in TFA and FFA for [1-(13)C] C16:0, while they were 0.60 ± 0.15% and 0.51 ± 0.11% for [1-(13)C] C18:1 (mean ± sem). By studying the kinetics of lipid excretion from subjects, two groups emerged. The first one showed rapid excretion in stool #1, whereas the second showed slower excretion in stools #2-#3. A significant difference was found in the FFA in stool #1 for C16:0 (p < 0.01) and C18:1 (p < 0.05). Individual excretion kinetics showed marked variability. Nevertheless, the CTR over the 3-day study period was substantial and homogenous for all subjects. These results confirm that the assessment of faecal elimination is of great importance when establishing total lipid distribution during the postprandial period and validate the analysis of cumulative tracer loss during 72 h post-tracer ingestion.     

Application of biosynthetic 13C-enrichment using [1-13C]-, [2-13C]- and [1,2-13C2]-acetate as precursor for 13C NMR spectral assignment of higher plant metabolites. The assignments of some bryonolic acid derivatives

The ¹³C NMR spectra of some derivatives of bryonolic acid (1) (D:C-friedoolean-8-en-3β-ol-29-oic acid) were assigned by means of ¹³C-enrichment, lanthanide-induced shifts (LIS) and comparison of chemical shift data between derivatives. The ¹³C-enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1-¹³C]-, [2-¹³C]- or [1,2-¹³C₂]-acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl-3β,29-diols (3,29-diacetyl-D:C-friedoolean-8-en-β,29-diol) 5, 5a, 5b and 5c, and 3-acetyl-3β,29-diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their ¹³C NMR spectra were recorded. The ¹³C concentration of the ¹³C-enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C-29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D- and E-ring carbons and those of the methyl carbons linked to these rings.     

Synthesis, complete 1H and 13C NMR assignment and crystal structure of novel epoxide derivatives of cytochalasin B

Five novel epoxide derivatives of cytochalasin B were synthesized. Reaction of cytochalasin B with t-BHP and BuLi led to selective epoxidation of the C-21/22 double bond to give a single monoepoxide, while reaction with m-CPBA yielded two diepoxides. Reaction of the monoepoxide with m-CPBA yielded two triepoxides. The relative configurations of the epoxides were elucidated by analogy with the natural product by means of spectroscopic methods; full assignment of NMR signals was achieved, and the absolute configuration was confirmed by X-ray crystallography.     

Fused s-triazino heterocycles. XIV 8H-1,3,7,8,9,10c-hexaazacyclopenta[a]phenalene, 1,3,7,8,10,11c-hexaazabenz[de]anthracene and 13H-4,6,8,13a, 13c-pentaazabenzo[de]naphthacene,three new ring systems

The synthesis of the title compounds 3,4 and 5 is described, using 7,9-dibromo-5-tribromomethyl-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene 2a as starting material. The key intermediates are 7,9-dibromo-2-t-butyl-4-cyano-5-hydrazino-1,3,6,9b-tetraazaphenalene 2b , 5-benzamidino-7,9-dibromo-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene 2c , and 7,9-dibromo-2-t-butyl-5-(2-carboxyanilino)-4-cyano-1,3,6,9b-tetraazaphenalene 2e.