Search results for "Epimer"
showing 10 items of 41 documents
ChemInform Abstract: Synthesis of Elemane Bis-lactones from Santonin - Synthesis of the Reported Structure of seco-Isoerivanin Pseudo Acid and Formal…
2001
The synthesis of the reported structure for seco-isoerivanin pseudo acid (1) and of an elemane bis-lactone 5 from santonin (4) through a common vinylic precursor 12 is described. Compound 5 is a known intermediate in a previous synthesis of the antitumor compound (+)-8-deoxyvernolepin (3). The vinyl group of 12 underwent a regio- and diastereoselective anti addition of an external electrophile and an intramolecular condensation to yield either the selenolactone 13 or the hydroxylactone 17. The lactones 13 and 17 served as key intermediates in the total synthesis of 1 and 5 respectively. A revision of the structure of seco-isoerivanin pseudo acid to the C-10 epimer is suggested on the basis …
The C-12 and C-20 configurations of some neo-clerodane diterpenoids isolated from Teucrium species
1986
Abstract A convenient and conclusive method for determining the C-12 stereochemistry of neo-clerodan-20,12-olide derivatives, even when only one epimer is available, is by 1H NMR NOE measurements. The C-12 configuration of 26 neo-clerodane diterpenoids isolated from Teucrium species has been re-examined by using this type of experiment. The results indicated that all the previous assignments were correct, except for teupyreinin, where the previously assigned C-12(S) configuration must be amended to C-12(R). This was confirmed by chemical transformations and additional 1H and 13C NMR studies. Furthermore, the NOE experiments allowed the assignment of a C-20(S) configuration for teuflavin, th…
Synthesis of various natural 8,12-elemanolides from artemisin
1989
Abstract This paper describes the chemical transformations of artemisin into various natural 8,12-elemanolides.
An approach to erythrophleum alkaloids. Synthesis of methyl (−)-4-epi-cassamate
1986
Abstract A synthetic approach to Erythrophleum alkaloids, involving as a key-step the regiospecific deprotonation of the ketone 5a, is described.
Synthesis of Optically Active N-(4-Hydroxynon-2-enyl)pyrrolidines: Key Building Blocks in the Total Synthesis of Streptomyces coelicolor Butanolide 5…
2021
AbstractStarting from 5-methylhexanal and (S)-configured N-propargylprolinol ethers, coupling delivered N-(4-hydroxynon-2-ynyl)prolinol derivatives as mixtures of C4 diastereomers. Resolution of the epimers succeeded after introduction of an (R)-mandelic ester derivative and subsequent HPLC separation. Alternatively, suitable oxidation gave the corresponding alkynyl ketone. Midland reagent controlled diastereoselective reduction afforded a defined configured propargyl alcohol with high selectivity. LiAlH4 reduction and Mosher analyses of the allyl alcohols enabled structure elucidation. The suitably protected products are used as key intermediates in enantioselective Streptomyces γ-butyrola…
NonclassicalPschorr andSandmeyer Reactions in Pyrazole Series
2005
The diazonium salt derived from 4-amino-N,1,3-trimethyl-N-(3-methyl-1-phenyl-1H-pyrazol-5-yl)-1H-pyrazole-5-carboxamide (14) was reacted with a mixture of CuSO4 and NaCl, with ascorbic acid as an initiator to afford the planar derivative 4,6-dihydro-1,4,6,8-tetramethyl-3-phenyldipyrazolo[3,4-b:4′,3′-d]pyridin-5(3H)-one (16) and its unexpected isomer 4,6-dihydro-3,4,6,8-tetramethyl-1-phenyldipyrazolo[4,3-b:4′,3′-d]pyridin-5(1H)-one (17), as well as the epimers (3S,4S)- (or (3S,4R)-) and (3S,4R)- (or (3S,4S)-) 4-chloro-2,4-dihydro-1′,3′,5,5′-tetramethyl-2-phenylspiro[pyrazole-3,4′(1′H)-pyrrolo[3,4-c]pyrazol]-6′(5′H)-one (18a and b, respectively). Epimers 18a and b were converted under basic c…
Foetidissimosides C–F, Novel Glycosides from the Roots ofCucurbita foetidissima
2004
Two novel echinocystic acid (=(3β,16α)-3,16-dihydroxyolean-12-en-28-oic acid) glycosides, foetidissimosides C (1), and D (2), along with new cucurbitane glycosides, i.e., foetidissimosides E/F (3/4) as an 1 : 1 mixture of the (24R)/(24S) epimers, were obtained from the roots of Cucurbita foetidissima. Their structures were elucidated by means of a combination of homo- and heteronuclear 2D-NMR techniques (COSY, TOCSY, NOESY, ROESY, HSQC, and HMBC), and by FAB-MS. The new compounds were characterized as (3β,16α)-28-{[O-β-D-glucopyranosyl-(13)-O-β-D-xylopyranosyl-(14)-O-6-deoxy-α-L-mannopyranosyl-(12)-α-L-arabinopyranosyl]oxy}-16-hydroxy-28-oxoolean -12-en-3-yl β-D-glucopyranosiduronic acid (1…
Foetidissimosides C—F, Novel Glycosides from the Roots of Cucurbita foetidissima.
2004
Two novel echinocystic acid (=(3β,16α)-3,16-dihydroxyolean-12-en-28-oic acid) glycosides, foetidissimosides C (1), and D (2), along with new cucurbitane glycosides, i.e., foetidissimosides E/F (3/4) as an 1 : 1 mixture of the (24R)/(24S) epimers, were obtained from the roots of Cucurbita foetidissima. Their structures were elucidated by means of a combination of homo- and heteronuclear 2D-NMR techniques (COSY, TOCSY, NOESY, ROESY, HSQC, and HMBC), and by FAB-MS. The new compounds were characterized as (3β,16α)-28-{[O-β-D-glucopyranosyl-(13)-O-β-D-xylopyranosyl-(14)-O-6-deoxy-α-L-mannopyranosyl-(12)-α-L-arabinopyranosyl]oxy}-16-hydroxy-28-oxoolean -12-en-3-yl β-D-glucopyranosiduronic acid (1…
Synthesis of Elemane Bis-Lactones from Santonin – Synthesis of the Reported Structure ofseco-Isoerivanin Pseudo Acid and Formal Synthesis of (+)-8-De…
2000
The synthesis of the reported structure for seco-isoerivanin pseudo acid (1) and of an elemane bis-lactone 5 from santonin (4) through a common vinylic precursor 12 is described. Compound 5 is a known intermediate in a previous synthesis of the antitumor compound (+)-8-deoxyvernolepin (3). The vinyl group of 12 underwent a regio- and diastereoselective anti addition of an external electrophile and an intramolecular condensation to yield either the selenolactone 13 or the hydroxylactone 17. The lactones 13 and 17 served as key intermediates in the total synthesis of 1 and 5 respectively. A revision of the structure of seco-isoerivanin pseudo acid to the C-10 epimer is suggested on the basis …
A Carbohydrate-Based Julia–Kocienski Reagent for Syntheses of Chain-Extended and C-Linked Saccharides
2014
The carbohydrate-derived Julia–Kocienski reagent 2-{[(3aS,4S,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]methylsulfonyl}-1,3-benzothiazole (6) was prepared from d -ribose and investigated in the eponymous olefination. The base-promoted generation of the Julia anion induced a rearrangement to the corresponding l -lyxose epimer 2-{[(3aS,4R,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]methylsulfonyl}-1,3-benzothiazole (12), which reacted readily with aldehydes and with a gluconolactone. The latter reaction furnished an exo-glycal-linked C-diglycoside.