摘要:

Electrochemical Decarboxylation ofL‐Threonine and Oligopeptide Derivatives with Formation ofN‐Acyl‐N, O‐acetals: Preparation of Oligopeptides with Amide or Phophonate C‐TerminusDerivatives of α‐amino acids with two stereogenic centers (cf.L‐threonine) and of di‐, tri‐, and tetrapeptides are electrolyzed in MeOH or AcOH, with formation ofN‐acyl‐N, O‐acetals (1b–15b,20b), in an anodic oxidative substitution of the COOH by an OR group. The amine ends of the oligopeptides may be benzyloxycarbonyl(Z)‐ or (tert‐butoxy)carbonyl(Boc)‐protected. With unprotected dipeptides, an electrolytic decarboxylative cyclization to imidazolidinones (18c,19c) may also occur (in H2O/NH4OAc). The electrolyses are carried out in simple flasks with cooling jackets (‘undivided cell’), using constant current conditions and anodes of Pt or glassy C. The electrolyte is generatedin situby adding 10–20 mol‐% of a tertiary amine. Mild acidic hydrolysis of electrolysis products thus obtained may lead to amino‐acid amides or peptide amides (10c, 11c, 12c, 17c) with one amino acid less than the starting material. The N, O‐acetals fromL‐threonine and the oligopeptides also react with organometallic nucleophiles such asGrignardcompounds (→21–26,29), with formation of products in which the original COOH group has been replaced by alkyl or allyl (sometimes even with moderate stereoselectivity). By treatment of the peptide‐derived (open‐chain) N, O‐acetals with trialkyl or triaryl phosphites/TiCl4the RO group is replaced by a phosphodiester group in a (non‐diastereoselective)Michaelis‐Arbuzov‐type reaction (1d,1e,2d–9d,5e). Thus, the two‐step sequence of electrolysis and phosphonation converts an oligopeptide derivative to an analogue with a phosphonic‐acid end group. The diastereoisomericN‐protected dimethyl and diethyl dipeptidephosphonates (also prepared from the corresponding diaryl esters by Ti(OR)4‐mediated transesterification) could be separated by preparative HPLC (SiO2,Lichrosorb Si 60, 10 μm); the dextrorotatory isomers of1d–3dwere assignedL,D‐, the laevoratory onesL,L‐configuration by hydrolysis to and identification of the known amino and aminophosphonic acids. The results described demonstrate a new simple route leadi

ISSN:0018-019X    

DOI:10.1002/hlca.19890720302

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

Hormaomycin, a Novel Peptide Lactone with Morphogenetic Activity on StreptomycesA culture identified asStreptomyces griseoflavus(strain W‐384) has been found to produce a novel peptide‐lactone antibiotic designated hormaomycin (6). The empirical molecular formula of the compound is established to be C55H69ClN10O14. The constituent amino acids of the antibiotic are suggested to be allothreonine (1; 1), isoleucine (2; 1), 3‐methyl‐phenylalanine (3; 2), and, for the first time identified from a natural source, 4‐[(Z)‐prop‐1‐enyl]‐proline (4; 1) and 3‐(2‐nitrocyclopropyl)‐alanine (5; 2). The amino acids were delivered by acidic hydrolysis and assigned by high‐resolution‐ GC/MS analysis (after transformation to derivatives) in combination with extended 2D‐NMR experiments of the antibiotic itself. From the latter, it became plausible that the N‐terminus of the peptide chain is acylated by a Cl‐containing derivative of 1H‐pyrrol‐2‐carboxylic acid. Hormaomycin is active against someGram‐positive bacteria. In addition, the antibiotic exhibits potent aerial mycelium‐inducing activit

ISSN:0018-019X    

DOI:10.1002/hlca.19890720303

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractFurther investigation of global extracts from cultures of the marine deuteromyceteDendryphiella salinaleads to the isolation of three novel trinor‐eremophilanes esterified by branched C9‐carboxylic acids, dendryphiellinB(= (+)‐(1R*,2S*,7R*,8aR*)‐1,2,6,7,8,8a‐hexahydro‐7‐hydroxy‐1,8a‐dimethyl‐6‐oxonaphthalen‐2‐yl (6R*, 2E, 4E)‐6‐hydroxy‐6‐methylocta‐2,4‐dienoate; (+)‐2), dendryphiellin C (=(+)‐(1R*, 2S*, 7R*, 8aR*)‐1,2,6,7,8,8a‐hexa‐hydro‐7‐hydroxy‐1,8a‐dimethyl‐6‐oxonaphthalen‐2‐yl (6S, 2E, 4E)‐6‐methylocta‐2,4‐dienoate; (+)‐3)), and dendryphiellin D (=(+)‐(1R*, 2S*, 7R*, 8aR*)‐1,2,6,7(8,8a‐hexahydro‐7‐hydroxy‐1,8a‐dimethyl‐6‐oxonaphthalen‐2‐yl (6R*,2E,4E)‐6‐(hydroxymethyl)octa‐2,4‐dienoate; (+)‐4). An intact eremophilane, dendryphiellin E (5), and its ethanolysis product dendryphiellin F whose absolute configuration is represented by structural formula (+)‐6are also isolated from the above extracts. Dendryphiellin E exists as an open form5ain equilibrium with a closed form5b. A similar equilibrium exists between the open form8aand the closed form8bof a non‐esterified eremophilane, dendryphiellin G (8), which is isolated too from the above extracts and proves structurally related to the cyclic portion of5. Finally, the free, branched C9‐carboxylic acids dendryphiellic acid A ((+)‐9) and B ((

ISSN:0018-019X    

DOI:10.1002/hlca.19890720304

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractAcetylenic acetals of typeI(Scheme 1)and acetylenic ketones of typeIII(Scheme 1),37and38(Scheme 7)are versatile synthetic precursors for the synthesis of various heterocycles by acid‐catalyzed cyclization reactions. By this way, substituted 3‐halofurans of typeIIandIV(Scheme 1)and flavones and styrylchromones(Scheme 7)can be synthesized in good‐to‐excellent yields. The high degree of regioselectivity in the synthesis of the 3‐halofurans(Scheme 4)is the result of the regioselective β‐addition of HX (X = Cl, Br, I) to the acetylenic aldehyde and acetylenic ketone moieties. A possible mechanism is depicted inScheme 5. Since 3‐halofurans can easily be metalated and substituted, this approach constitutes a new synthesis of highly subs

ISSN:0018-019X    

DOI:10.1002/hlca.19890720305

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

A New Azepine‐Ring SynthesisA new one‐step synthesis of an azepine ring is described. The 2H‐pyran‐2‐one ring of methyl cumalate (8) or cumalaldehyde (2) upon reaction with an 1‐aminoacryl derivative, e.g.1or6, is opened with subsequent decarboxylation to give a 1‐aminobutadiene derivative that undergoes an electrocyclic ring closure to the azepine ring (S

ISSN:0018-019X    

DOI:10.1002/hlca.19890720306

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractThe crude petroleum‐ether extract of the root bark ofHypericum revolutumVAHL(Guttiferae) exhibitedin vitrogrowth‐inhibitory activity against the Co‐115 human colon carcinoma cell line. Activity‐guided fractionation of this extract resulted in the isolation of two new hyperforin derivatives1and2. The structure of1(hyperevolutin A) was established by X‐ray analysis as the 4‐hydroxy‐8‐exo‐methyl‐5,7‐exo‐bis(3‐methylbut‐2‐enyl)‐1‐(2‐methyl‐1‐oxopropyl)‐8‐endo‐(4‐methylpent‐3‐enyl)bicyclo[3.3.1]non‐3‐ene‐2,9‐dione. The structure of the homologue2was deduced by co

ISSN:0018-019X    

DOI:10.1002/hlca.19890720307

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractIn the present study, it is confirmed that the deuteration of CH groups is accompanied by a small but genuine decrease in lipophilicity. The lipophilicity of deuterated isotopomers of caffeine was measured by reversed‐phase HPLC. Overall, lipophilicity was shown to decrease when going from unlabelled caffeine to the three isomeric trideuterated caffeines, then to the three isomeric hexadeuterated caffeines, and finally to nonadeuterated caffeine. In addition, position‐specific effects were also proven.E.g.(7‐methyl‐2H3)caffeine experienced a smaller isotope effect than its two positional isomers. Both a cavity factor (decreased volume of deuterated isotopomers) and intramolecular electronic effects are postulated t

ISSN:0018-019X    

DOI:10.1002/hlca.19890720308

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractThe new linear triamine 2,6‐bis(pyrrolidin‐2‐yl)pyridine (II) has been synthesized, and the (R,S)‐, (R,R)‐, and (S,S)‐isomers have been separated. Compared to other triamines showing a similar structure, these new ligands form very stable Cu2+complexes. No significant difference is observed between themesoand the racemic forms for their binary or ternary mixed‐ligand complexes with the amino acids alanin

ISSN:0018-019X    

DOI:10.1002/hlca.19890720309

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractStarting from sultam1, the chiral dienophile (2R)‐N‐glyoxyloylbornane‐10,2‐sultam (4) was readily prepared. Non‐catalyzed atmospheric‐ and high‐pressure as well as [Eu(fod)3]‐promoted [4 + 2]cycloadditions of 1‐methoxy‐buta‐1,3‐diene (5) to chiral dienophile4, leading with high asymmetric induction to 6‐methoxy‐3,6‐dihydro‐2H‐pyran‐2‐yl derivatives6–9, are described. The extent and direction of asymmetric induction in these reactions were established by1H‐NMR analysis and chemical correlation, respectively. Stereochemical models for both non‐catalyzed and

ISSN:0018-019X    

DOI:10.1002/hlca.19890720310

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY

摘要:

AbstractIn a search for further synthetic routes to substituted [5.5.5.5] fenestranes, compound1a, a derivative of 7‐methoxyindane, was photolyzed. Two of the three photoproducts,viz.the [3.5.5.5]fenestrane3aand the isomer4a, are formed according to the expected intramolecularmeta‐cycloaddition. A different mechanism is suggested for the formation of the major componen

ISSN:0018-019X    

DOI:10.1002/hlca.19890720311

出版商:WILEY‐VCH Verlag GmbH    

年代:1989

数据来源: WILEY