Biosynthesis of cytochalasans. Part 4. The mode of incorporation of common naturally-occurring carboxylic acids into cytochalasin D1.

Utilization of sodium [1-¹⁴C]-, [2–¹⁴C]-, and [1,2-¹³C]-acetates, [1-¹⁴C]-, [1-¹³C]-, or [2-¹⁴C]-propionates, [1-¹⁴C]-or [2-¹⁴C]-malonates, of [1-¹⁴C]- or of [1-¹⁴C]-myristic acid, or of [1-¹⁴C]- and [1-¹⁴C]-palmitic acid in the biosynthesis of cytochalasin D ( 1 ) by Zygosporium masonii was determined by degradation studies or by carbon magnetic resonance spectroscopy. The precursors were incorporated primarily via the acetate-malonate pathway to generate 1 from nine intact acetate units, eight of which are coupled in a head to tail fashion to form the C₁₆-polyketide moiety.     

Studies on the Biosynthesis of Spirostaphylotrichin A

Incorporation of ¹⁴C-labelled acetate and amino acids as well as of [1-¹³C]-, [2-¹³C]-, and [1,2-¹³C₂] acetate, L -[methyl¹³C] methionine, [2,3-¹³C₂] succinate, and L -[2,3-¹³C₂] aspartate into spirostaphylotrichin A ( 1 ) by Staphylotrichum coccosporum demonstrates that the building blocks of 1 are 5 units of acetate/malonate, 1 unit of methionine, and a C₄-dicarboxylic acid. The latter is most likely aspartate and derived from the citric-acid cycle. Using [2-¹³C, 2-²H₃] acetate as a precursor, the starter unit of the polyketide chain was identified.     

Biosynthesis of the Verrucarins and Roridins. Part 1. The transformation of mevalonic acid into verrucarinic acid. Evidence for a hydrogen 1,2-shift. Verrucarins and roridins, 27th communication

Incorporation experiments using sodium [2-¹⁴C]-, [2-³H]-, (3R)-[5-¹⁴C]- and [2-³H, 2-¹⁴C]-mevalonates and with mevalonates stereospecifically tritiated at C(2) demonstrate the transformation of mevalonic acid ( 8 ) into verrucarinic acid ( 5 ). Degradation experiments showed that this transformation occurs with a hydrogen 1, 2-shift of the ‘pro-2R’ hydrogen atom of mevalonate to C(3) of verrucarinate. A possible mechanistic pathway is discussed.     

Biosynthesis of the Cytochalasans. Biosynthetic studies on chaetoglobosin A and 19-O-acetylchaetoglobosin A

Incorporation of [1-¹³C]-, [2-¹³C]- and [1,2-¹³C₂]-acetate, [1-¹³C]-propionate, [¹³C-CH₃]-L -methionine and [3-¹⁴C]-DL -tryptophan into chaetoglobosin A ( 1 ) and 19-O-acetylchaetoglobosin A ( 2 ) by Chaetomium globosum demonstrated that the building blocks of 1 and 2 are 9 and 10 units of acetate/malonate respectively, 3 units of methionine and 1 unit of tryptophan. Propionate is incorporated indirectly after several biological transformations. Using [2-¹³C, 2-²H₃]-acetate as precursor, the starter unit of the polyketide-chain was identified. Experiments which [¹³C, ²H₃-CH₃-L -methionine demonstrated that the three C-methylations occur with retention of all three H-atoms of the methyl group. Incorporation experiments with various ¹⁴C- and ³H-labelled tryphtophan samples and with [2-²H]- and [2-¹⁵N]-L -tryptophan showed that the amino acid is incorporated intact with retention of both the α-H- and the α-N-atom. On the basis of these results a more detailed general scheme of the cytochalasan biogenesis is proposed.     

cis,cis,cis‐(Acetato‐O,O′)­bis­[1,2‐bis­(di­phenyl­phosphino)­ethane‐P,P′]­ruthenium(II) hexa­fluoro­phosphate di­methanol solvate

In the cation of the title complex, cis,cis,cis‐[Ru(η²‐O₂CMe)(dppe)₂]PF₆·2MeOH [dppe is 1,2‐bis­(di­phenyl­phosphino)­ethane, C₂₆H₂₄P₂], the Ru atom is in a pseudo‐octahedral coordination environment with two chelating dppe ligands and one chelating acetate ligand. Intra‐phosphine and intra‐acetate bond lengths and angles are unexceptional. Deviations from idealized octahedral coordination angles at ruthenium [O—Ru—O 59.43 (8)° and P—Ru—P 103.19 (2)°] presumably derive from constraints imposed by the chelate rings. The Ru—P distances for the mutually trans P‐donor atoms [2.3785 (6) Å] are significantly longer than those for the Ru—P linkages trans to the acetate ligand [2.3074 (6) Å]. The Ru1, C1 and C2 atoms lie on a twofold axis, and atom P3 of the anion lies on an inversion centre.     

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.     

Biosynthesis of brefeldin A

By feeding growing cultures of Penicillium brefeldianum Dodge with [-¹⁴C]-acetate radioactive brefeldin A (C₁₆H₂₄O₄) was obtained. By extensive degradation of [¹⁴C]-brefeldin A, the individual radioactivity of 12 of the 16 carbon atoms was determined quantitatively. The pattern of the distribution of the radioactivity shows that 8 acetate units have been incorporated into the metabolite in a regular manner. These findings suggest an octaketide as an intermediate. Possible mechanisms for the formation of the trans-fused cyclopentane ring are discussed.     

Biosynthesis of aspergiolide A, a novel antitumor compound by a marine-derived fungus Aspergillus glaucus via the polyketide pathway

Aspergiolide A, a novel antitumor compound, was produced by a marine-derived filamentous fungus Aspergillus glaucus. The biosynthesis of it was unambiguously determined by feeding experiments using [l-¹³C]sodium acetate, [2-¹³C]sodium acetate, and [1,2-¹³C₂]sodium acetate precursors followed by ¹³C NMR spectroscopic investigation of the isolated products. Analysis of the patterns of ¹³C-enrichment revealed that all 25 carbon atoms in skeleton of aspergiolide A were derived from labeled acetate. And among them, 12 carbon atoms were labeled from the carboxylic group of acetate, while the other 13 carbon atoms were labeled from the methylic group of acetate. Besides, the labeling pattern of [1,2-¹³C₂]sodium acetate feeding experiment demonstrated that 12 intact acetate units were incorporated in aspergiolide A by polyketide pathway.     

Die thermische Umlagerung von 2-(Buta-1′,3′-dienyl)-phenolen in 2-Alkyl-2H-chromene; Beispiele für aromatische [1,7a]- und [1,5s]sigmatropische Wasserstoffverschiebungen

2-(1′-cis,3′-cis-)- and 2-(1′-cis,3′-trans-Penta-1′,3′-dienyl)-phenol (cis, cis- 4 and cis, trans- 4 , cf. scheme 1) rearrange thermally at 85–110° via [1,7 a] hydrogen shifts to yield the o-quinomethide 2 (R ? CH₃) which rapidly cyclises to give 2-ethyl-2H-chromene ( 7 ). The trans formation of cis, cis- and cis, trans- 4 into 7 is accompanied by a thermal cis, trans isomerisation of the 3′ double bond in 4. The isomerisation indicates that [1,7 a] hydrogen shifts in 2 compete with the electrocyclic ring closure of 2 . The isomeric phenols, trans, trans- and trans, cis- 4 , are stable at 85–110° but at 190° rearrange also to form 7 . This rearrangement is induced by a thermal cis, trans isomerisation of the 1′ double bond which occurs via [1, 5s] hydrogen shifts. Deuterium labelling experiments show that the chromene 7 is in equilibrium with the o-quinomethide 2 (R ? CH₃), at 210°. Thus, when 2-benzyl-2H-chromene ( 9 ) or 2-(1′-trans,3′-trans,-4′-phenyl-buta1′,3′-dienyl)-phenol (trans, trans- 6 ) is heated in diglyme solution at >200°, an equilibrium mixture of both compounds (～ 55% 9 and 45% 6 ) is obtained.     

Syntheses of Unique Bicyclophostones and Unexpected Difference in the Reaction of Lawesson's Reagent vs. P2S5 with Cis-Bicyclophostone (1)

Abstract

The purpose of this study was to synthesize trans-l and determine the equilibriurr constant with cis-1. Oniy the synthesis¹ and x-ray structure² of the cis isomer have bcen reported. Four prior synthetic routes to make the vans isomer³ gave only cis product. For example, intrarmolecular ring closure of the cis or trains isomers of 4 (R= (CH₂)₃OH) with LiH or thermal closure of the cis or trans 4 (R= (CH₂)₂) gave only cis-1. Since both iosmers of 1,8-dioxabicyclo[4.4.0] decane are known and readily equilibrate (57% cis and 43% trans), the apparent inaccessibility of trans-1 attracted our attention. Thc preparation of trans-1 was achieved by treatment of cis-1 with Lawesson's reagent (LR) to provide cis-2. followed by oxidation with m-chloroperbenzoic acid/trifluoroacetic acid to give a 5:1 mixture of cis:trans 1, respectively. An unexpected formation of the sulfur analogue of 1 was observed on treatment of cis-1 with P₂S₅/pyridine at reflux temperatures to give a 1.6:1 mixture of cis:trans 3, respectively. Thermal quilibration of 1 at 204°C provided an equilibrium ratio of 99.5% cis and 0.5% of the trans isomer. However, equilibration of 3 at 250°C led to 82.2:17.8 ratio in favor of the cis isomr. These results are consistent with semiemperical MO calculations. The stereochemical outcome on treatment of 4 with LR was also investigated. X-ray structures for six compounds: trans-1, cis-2, cis and trans-3; cis-4 (R=Ph), and cis-5, (R = Ph) wen determined.     

Biosynthesis of cytochalasins. II Building blocks of cytochalasun D

A number of potential ¹⁴C- and ³H-labelled precursors were fed to growing cultures of Zygosporium masonii after the rate of formation of cytochalasin D had been measured. By chemical degradation of [¹⁴C]- and [³H, ¹⁴C]-cytochalasin D the distribution of the radioactivity originating from incorporated [4′-3H, U-¹⁴C]-L -phenylalanine and [CH₃-¹⁴C]-L -methionine was determinated. The results demonstrate that the building blocks of cytochalasin D are 1 unit of pheylalanine, 3 units of methionine and acetate units.     

Spectroscopic Evidence of in situ Formation of a Novel Tetrakis(Tetrazolato)Iron Compound

In an attempt to synthesize the complex [Fe(CN)₅(N₂)]^3- by reaction of Na[Fe(CN)₅(NO)]·2H₂O with azide followed by treatment with NO[SbCl₆], a similar method to that used by Feltham to obtain trans-[RuCl(N₂)(das)₂]Cl₂ from trans-[RuCl(NO)(das)₂]Cl₂, we found spectroscopic evidence that excess azide reacts with the CN^- ligands to generate tetrazolato groups C-coordinated to Fe. Initial results suggest that the obtained compound is sodium azidotris(2H-tetrazolato)(5H-tetrazolato)iron(0). The spectroscopic evidence also indicates that these heterocycles are destroyed by reaction with NO[SbCl₆], and the CN^- groups are regenerated. Here we present the characterization of these complexes by IR, ¹³C NMR, conductivity measurements, elemental analysis and magnetic susceptibility.     

Synthesis of 24-Methylidene[24-14C]- and 24-Methylidene[7-3H]cholesterol

The syntheses of 24-methylidene[24-¹⁴C]cholesterol ( 7a ) and of 24-methylidene[7-³H]cholesterol ( 7b ) from commercially available (20S)-3-oxopregn-4-ene-20-carbaldehyde ( 1 ) are described. The method also provides simple preparations of 3β-acetoxy[24-¹⁴C]chol-5-en-24-oic acid ( 4 ) and 24-oxocholest-5-en-3β-yl acetate ( 6b ).     

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.     

Light-induced cis/trans isomerization of cis-[Pd(L-S,O)2] and cis-[Pt(L-S,O)2] complexes of chelating N,N-dialkyl-N′-acylthioureas: key to the formation and isolation of trans isomers

Irradiation cis-[M(Lⁿ-S,O)₂] complexes (M = Pt^II, Pd^II) derived from N,N-dialkyl-N′-benzoylthioureas (HLⁿ) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by ¹H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L²-S,O)₂] was directly monitored by ¹H NMR and ¹⁹⁵Pt NMR spectroscopy of selected cis-[Pt(L-S,O)₂] compounds in chloroform-d; both with and without light irradiation allows the δ(¹⁹⁵Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)₂] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution.     

Biosynthesis of phoslactomycins: cyclohexanecarboxylic acid as the starter unit

Phoslactomycins (PLMs) A-F, produced by actinomycetes are polyketide-type antibiotics derived from a hydroxycyclohexanecarboxylic acid or a cyclohexanecarboxylic acid starter unit. Feeding experiments with [2-¹³C]shikimic acid indicated that the C-18 carbon of PLMs comes from C-5 of shikimate. Further feeding studies of cis and trans-3-hydroxy[7-¹³C]cyclohexanecarboxylic acid, [7-¹³C]- and [²H₁₁]cyclohexanecarboxylic acid have suggested that the starter unit in the PLM biosynthesis is not cis-3-hydroxycyclohexanecarboxylate but cyclohexanecarboxylate and that PLM-B is produced initially, and subsequently converted to other analogs by hydroxylation and acylation.     

Chiral [2H]-Labelled Methylene Groups in Trienoic- and Dienoic Fatty Acids: A Facile Approach via Asymmetric Epoxidation of [2H] Allyl Alcohols

Chiral [²H] -labelled methylene groups flanked by two double bonds within (poly)unsaturated fatty acids are readily available from trans-2,3-epoxy[2,3-²H₂] alk-4-yn-l-ols, obtained in their turn by asymmetric epoxidation of the corresponding (E)-[2,3-²H₂] alk-2-en-4-yn-l-ols (see Scheme 3). The procedure is exemplified for (8S,3Z,6Z,9Z)-[7,8-²H₂] trideca-3,6,9-trienoic acid ((8S)- 11 ) and (8R)- 11 (Scheme 4) as well as for (5S,3Z,6Z)-[4,5^?2H₂]deca-3,6-dienoic acid ((5S)- 13 ) and (5R)- 13 (Scheme 5).     

Synthesis of an Isotopically Isomeric Mixture of 1,4,6,8-Tetramethyl[13C2]azulene and Its Thermal Reaction with Dimethyl Acetylenedicarboxylate

Sodium [1,3-¹³C₂]cyclopentadienide in tetrahydrofuran (THF) has been prepared from the corresponding labelled [¹³C₂]cyclopentadiene which was synthesized from ¹³CO₂ and (chloromethyl)trimethylsilane (cf. Scheme 10) according to an established procedure. It could be shown that the acetate pyrolysis of cis-cyclopentane-1,2-diyl diacetate (cis- 22 ) at 550 ± 5° under reduced pressure (60 Torr) gives five times as much cyclopentadiene as trans- 22 . The reaction of sodium [1,3-¹³C₂]cyclopentadienide with 2,4,6-trimethylpyrylium tetrafluoroborate in THF leads to the formation of the statistically expected 2:2:1 mixture of 4,6,8-trimethyl[1,3a-¹³C₂], -[2,3a-¹³C₂]-, and -[1,3-¹³C₂]azulene ( 20 ; cf. Scheme 7 and Fig. 1). Formylation and reduction of the 2:2:1 mixture [¹³C₂]- 20 results in the formation of a 1:1:1:1:1 mixture of 1,4,6,8-tetramethyl[1,3-¹³C₂]-, -[1,3a-¹³C₂]-, -[2,3a-¹³C₂]-, -[2,8a-¹³C₂]-, and -[3,8a-¹³C₂]azulene ( 5 ; cf. Scheme 8 and Fig. 2). The measured ²J(¹³C, ¹³C) values of [¹³C₂]- 20 and [¹³C₂]- 5 are listed in Tables 1 and 2. Thermal reaction of the 1:1:1:1:1 mixture [¹³C₂]- 5 with the four-fold amount of dimethyl acetylenedicarboxylate (ADM) at 200° in tetralin (cf. Scheme 2) gave 5,6,8,10-tetramethyl-[¹³C₂]heptalene-1,2-dicarboxylate ([¹³C₂]- 6a ; 22%), its double-bond-shifted (DBS) isomer [¹³C₂]- 6b (19%), and the corresponding azulene-1,2-dicarboxylate 7 (18%). The isotopically isomeric mixture of [¹³C₂]- 6a showed no ¹J(¹³C,¹³C) at C(5) (cf. Fig. 3). This finding is in agreement with the fact that the expected primary tricyclic intermediate [7,11-¹³C₂]- 8 exhibits at 200° in tetralin only cleavage of the C(1)? C(10) bond and formation of a C(7)? C(10) bond (cf. Schemes 6 and 9), but no cleavage of the C(1)? C(11) bond and formation of a C(7)? C(11) bond. The limits of detection of the applied method is ≥96% for the observed process, i.e., [1,3a-¹³C₂]- 5 + ADM→ [7,11-¹³C₂]- 8 →[1,6-¹³C₂]- 9 →[5,10a-¹³C₂]- 6a (cf. Scheme 6).     

Differential Hydrogen Exchange During Biosynthesis of Cytochalasins B and D

Sodium [2-¹³C,2-²H₃]acetate was incorporated into cytochalasin B( 1 ) by Phoma exigua and into cytochalasin D ( 2 ) by Zygosporium masonii. The ¹³C-NMR. and ²H-NMR. of the metabolites showed that most of the deuterium was lost except at carbon atoms which are in polyketide chain-initiating units.     

Elucidation of the Reaction Products of Acetonitrile with Phosphorus Pentachloride

Abstract

The reaction of acetonitrile with PCl, results in the ionic compounds (1) to (4) containing the trichloro[2-chloro-2-[(trichlorophosphoranyli-dene)amino]ethenyl]phosphorus cations and not in the compounds [CH2?C?NPCl₃]PCl₆1 or trichloro[2-chloro-1 -[(trichlorophosphoranyli-dene)amino] ethenyl]phosphorus hexachlorophosphate (5) as assumed from ³¹P-NMR spectra [2, 3]. The crystal structures of the compounds (1) to (4) were determined with X-rays at 95K. As observed for the CI-C(NPCl₃); cation all the cations show cis-trans conformations with respect to their CI-C-X-P torsion angles. The wcl3 groups of the cations have two different orientations with one C?N?P?CI torsion angle of about 0° (cis) as in (1) or about 180° (trans) as in (3) and (4). In the salt (2) there are two formula units in the asymmetric unit with one cation showing the cis and the other showing the tram conformation.