C(16)-C(18) Rearrangements of Steroid Alkaloids

Sheehan, John C.; Young, Richard L.; Cruickshank, Philip A.

doi:10.1021/ja01508a044

Cited by 20 publications

(18 citation statements)

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“…However, it should be noted that in this case the induced asymmetry cannot be directly based on the optical rotatory power of the Hydrogenation in the presence of Raney-Ni gave 6% optical purity for D-Phe (Sheehan & Chendler, 1961) recovered Phe. In fact, the specific rotatory power observed for the recovered Phe corresponds to an average value deriving from the asymmetric reductions of the two unsaturated residues enclosed in the tripeptide.…”

Section: Doubly Unsaturated Tripeptidesmentioning

confidence: 87%

“…The data reported in Table 2 show that the dehydro-Phe residue, which is farther from the asymmetric centre, affords GPhe in high optical yield. Several literature reports (Sheehan & Chendler, 1961;Nakayama et d., 1971;Hiskey & Northfop, 1965) have utilized the Prelog rule to predict the enantiomer which will be predomiaantly formed in asymmetric hydrogenation under the induction of a chiral centre already present in the molecule. Several literature reports (Sheehan & Chendler, 1961;Nakayama et d., 1971;Hiskey & Northfop, 1965) have utilized the Prelog rule to predict the enantiomer which will be predomiaantly formed in asymmetric hydrogenation under the induction of a chiral centre already present in the molecule.…”

Section: Doubly Unsaturated Tripeptidesmentioning

confidence: 99%

“…At present, two sets of data are available in the literature concerning catalytic hydrogenation of peptides containing one dehydro-Phe residue and a C-terminal optically active group: the resulting Phe showed, in one case the opposite absolute configuration (Sheehan & Chendler, 1961) and, in the second case, the same configuration (Nakayama et al, 1971) of the asymmetric carbon atom already present in the molecule.…”

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confidence: 99%

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Asymmetric Hydrogenation of Unsaturated Peptides

Pieroni¹,

Bacciola²,

Fissi³

et al. 1977

International Journal of Peptide and Protein Research

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Eleven unsaturated peptides, containing one or two dehydro-phenylalanyl (dehydro-Phe) residues and a C-terminal L-amino acid have been hydrogenated in the presence of palladium-on-charcoal. Hydrolysis o f the saturated peptides thus obtained gave optically active phenylalanine showing the occurrence of asymmetric induction during the hydrogenation. Both monoansaturated dipeptides and doubly unsaturated tripeptides with L-Glu, L-Leu and L-Val as chiral end-group afforded L-Phe in 40-50% optical yield. In the case of the trip ep t ide N-a ce ty I-(de hy dro -Ph e) -(dehy dro -Ty r) -L -Glu

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Section: Doubly Unsaturated Tripeptidesmentioning

confidence: 87%

Section: Doubly Unsaturated Tripeptidesmentioning

confidence: 99%

mentioning

confidence: 99%

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Asymmetric Hydrogenation of Unsaturated Peptides

Pieroni¹,

Bacciola²,

Fissi³

et al. 1977

International Journal of Peptide and Protein Research

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“…24) wurde in Anlehnung an Lit 29). aus 4.95 g (50 mmol) rerl-Butylisocyanat und 3.75 g (50 mmol) 2-Methoxyethanamin in 50 ml Dichlormethan erhalten.…”

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Photochemische Stickstoff‐Eliminierung aus 1‐(1‐Alkenyl)‐4‐tert‐butyl‐1,4‐dihydro‐5H‐tetrazol‐5‐onen. Konkurrenz zwischen Methanol‐Addition und Cyclisierung einer dipolaren Zwischenstufe

Quast

Nahr

1984

Chem. Ber.

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Aus dem 5-Chlortetrazol 7 und dem Tetrazolon 9 werden auf verschiedenen Wegen die 4-terlButyl-1-vinyltetrazolone 12a -c sowie die Tetrazolone 13 und 14 hergestellt . Bei der 254-nm-Photolyse der 1-Vinyltetrazolone 12 erhalt man in Abhangigkeit von Struktur und Reaktionsbedingungen das Imidazolon 16, die 4-Methoxyimidazolidinone 20 und/oder die N-(l,2-Dimethoxyalky1)harnstoffe 22. Die Ergebnisse sprechen fur eine Konkurrenz zwischen Cyclisierung The 4-ferr-butyl-1-vinyltetrazolones 12a -c and the tetrazolones 13 and 14 are synthesized from the 5-chlorotetrazole 7 and the tetrazolone 9 ria several routes. Bis(benzonitri1e)palladium dichloride catalyses the 0 + N-Claisen rearrangement 8 + l l , the ally1 -+ vinyl rearrangements l l a -. 12b and l l b * 1212, as well as rhe equilibration 13 t 14. On 254 nm photolysis of the vinyltetrazolones 12 nitrogen is extruded and cyclic and/or acyclic products of primary photointermediates are formed: In [D3]acetonitrile as solvent, 77% of 1-fert-butylimidazolone 16 arises from 12a, while the tetrazolones 12b, c produce only complex mixtures. In methanol as solvent, the methanol adduct 2Oa (23%) of the intermediate imidazolone 15a and the acyclic N-(1,2-dimethoxyethy1)urea 22a (32%) are obtained besides 45% of 16. In contrast, from 12c in methanol the corresponding urea 22c is formed almost quantitatively as the only product. In

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“…1.40 (s, CH3), 1.63 (s, CH3), 3.76 (s, OCH3), 4.03 (s, 3-H),4.70 (d, J = 2 Hz, 6-H or 5-H), 5.37 (d, J = 2Hz, 5-H or 6-H). This salt was then N-phenylacetylated by treatment of an ice-cooled suspension of 1.600 g (6 mmol) of 3cx in 45 ml of anhydrous methylene chloride with 6 ml of a solution containing 2.1 ml of triethylamine in 13 ml of methylene chloride, followed by simultaneous and dropwise addition of 7 ml of the triethylamine solution and of a phenylacetyl chloride solution (1.3 ml in 8.7 ml of methylene chloride).…”

mentioning

confidence: 99%

Preparation and isomerization of 5-epibenzylpenicillins

Busson¹,

Vanderhaeghe²

1976

J. Org. Chem.

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5-Epibenzylpenicillin methyl and benzyl ester were obtained by replacement of the phthalimido side chain of the corresponding 6-phthalimido-5-epipenicillanates, which were prepared from the natural isomer by the method of Kukolja. Base-catalyzed isomerization of silylated 5-epibenzylpenicillin methyl ester in the presence of triethylamine and DBN was investigated. With triethylamine, no epimerization was observed, whereas a mixture of 5 epimer and of the enantiomers of the 6 epimer and natural isomer was obtained when DBN was used as catalyst. These observations, which indicate an epimerization at position 3, are compared with the results of isomerizations of penicillanates with a different configuration and with other side chains. The general mechanism of epimerization of penicillanates is discussed. The antibiotic activity of the sodium salt of 5-epibenzylpenicillin, prepared by hydrogenolysis of the benzyl ester, is less than 0.1% of that observed for natural benzylpenicillin.

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C(16)-C(18) Rearrangements of Steroid Alkaloids

Cited by 20 publications

References 0 publications

Asymmetric Hydrogenation of Unsaturated Peptides

Asymmetric Hydrogenation of Unsaturated Peptides

Photochemische Stickstoff‐Eliminierung aus 1‐(1‐Alkenyl)‐4‐tert‐butyl‐1,4‐dihydro‐5H‐tetrazol‐5‐onen. Konkurrenz zwischen Methanol‐Addition und Cyclisierung einer dipolaren Zwischenstufe

Preparation and isomerization of 5-epibenzylpenicillins

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