Search results for "Hemiacetal"
showing 10 items of 13 documents
Enantioselective synthesis of 2-substituted-1,4-diketones from (S)-mandelic acid enolate and α,β-enones
2006
[EN] An approach for the synthesis of chiral non-racemic 2-substituted-1,4-diketones from (S)-mandelic acid and ¿,ß-enones has been developed. The reaction of lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with ¿,ß-unsaturated carbonyl compounds proceeds readily to give the corresponding Michael adducts in good yields and with high diastereoselectivities. The addition of HMPA (3 equiv) reverses and strongly enhances the diastereoselectivity of the reaction. A change in the reaction mechanism from a lithium catalyzed to the one where catalysis has been suppressed by coordination of HMPA to lithium is proposed to explain these resul…
‘One-Pot’ Synthesis of Raumacline from Ajmaline
1993
For the alkaloid raumacline (2), which is a biotransformation product of ajmaline (1) in Rauwolfia serpentina cell cultures, an efficient ‘one-pot’ synthesis was developed using a NaBH4/riboflavin/light-mediated transformation of 1 into 2 with a total yield of 86%.
Copper-Assisted Hemiacetal Synthesis: A Cu II Chain Obtained by a One-Step in situ Reaction of Picolinaldehyde
2014
International audience; The 1D polymer complex [Cu2(L)2(SCN)2]n (1 ) has been synthesised in a one‐step in situ reaction of picolinaldehyde with sodium thiocyanate. The complex 1 was characterised by FTIR spectroscopy, UV/Vis spectrophotometry and elemental analysis. The crystal structure of complex 1 shows that chains of dimer complexes are formed with tetra‐ and pentacoordinate copper centres alternately linked by one thiocyanato and two alkoxido bridges. Variable‐temperature magnetic measurements showed a strong antiferromagnetic interaction between the copper centres within the dimer mediated by the two alkoxido bridges with a J value of –374 cm–1, which is in agreement with the DFT‐cal…
Synthesis and comparison of the antiinflammatory activity of manoalide and cacospongionolide B analogues.
1998
We have synthesized analogues of two naturally occurring antiinflammatory marine compounds, manoalide and cacospongionolide B, containing a pyranofuranone moiety which is considered the pharmacophoric group. The two compounds, and hence their analogues, differ in the presence or absence in the dihydropyran ring of an hemiacetal function which was considered essential to irreversibly inactivate phospholipase A 2 (PLA 2 ). The two series of compounds were tested for their inhibitory effects on secretory PLA 2 belonging to the groups I, II, and III, and the activities were found to be similar in both series, irrespective of the presence or absence of the additional hemiacetal function. In addi…
Ferromagnetism in Cu II 4 and Co II 4 Complexes Derived from Metal‐Assisted Solvolysis of Di‐2,6‐(2‐pyridylcarbonyl)pyridine: Syntheses, Structures, …
2008
Metal-assisted solvolysis of di-2,6-(2-pyridylcarbonyl)pyr-idine (pyCOpyCOpy, dpcp) by M(0 2 CMe) 2 ·xH 2 O (M II = Cu II , CO II ) led to complex [Cu 4 {pyC(O) 3 pyC(O)(OEt )py}(O 2 CMe )5-(EtOH) 2 ] (1), when the reaction was carried out in EtOH, and to complex [Co4{pyC(O)(OMe )pyC(O)(OMe )py} 2 (02CMe)2-(N 3 ) 2 ] (2), when the reaction was carried out in MeOH in the presence of azide anions. Complex 1 consists of four Cu II ions bridged by the hemiacetal-gem-diol form of the ligand, which is found in a μ 4 -η 2 :η 2 :η 2 :η 1 :η 1 :η 1 coordination mode. It exhibits ferromagnetic couplings among all nearest neighbors and antiferromagnetic next-nearest-neighbor interactions (J 12 = J 1 =…
Minor diterpenoids from Scutellaria polyodon.
2000
Four minor neoclerodane diterpene constituents were isolated from the aerial parts of Scutellaria polyodon. These compounds were characterized as the new scupolins J (1) and K (2) and the previously known scutalpin O (3) and scutalsin.
Neoclerodane Diterpenoids from Scutellaria polyodon
1997
Nine new neoclerodane diterpenoids, scupolins A−I, have been isolated from an Me2CO extract of the aerial parts of Scutellaria polyodon (3−11), together with the known neoclerodanes jodrellin B (1) and scutecolumnin A (2). Structures 3−11 were established by spectroscopic means and by comparison with closely related compounds.
Synthesis and cytotoxic activity of novel C7-functionalized spongiane diterpenes.
2003
Based on two lead cytotoxic spongiane diterpenes, a new series of C7-oxygenated derivatives were synthesized and evaluated for their antitumor activity in vitro against the cancer cell lines HeLa and HEp-2. In general, introduction of either hydroxyl or acetoxy groups at C-7 did not improve the resultant cytotoxicity, while the presence of a butyrate ester led to more active compounds (CC(50)=4.0-9.5 microM).
ChemInform Abstract: Synthesis of Elemane Bis-lactones Structurally Related to Vernolepin.
2010
Abstract The chemical transformation of santonin into an elemane bis -lactone structurally related to the antitumour compound vernolepin is reported. The transformation of ring A of santonin into a hemiacetal δ-lactone was achieved in eleven steps. The spectroscopic characteristics of the synthetic product obtained in this way revealed that the proposed structure for the natural product should be revised.
Synthesis of elemane bis-lactones structurally related to vernolepin
1998
Abstract The chemical transformation of santonin into an elemane bis -lactone structurally related to the antitumour compound vernolepin is reported. The transformation of ring A of santonin into a hemiacetal δ-lactone was achieved in eleven steps. The spectroscopic characteristics of the synthetic product obtained in this way revealed that the proposed structure for the natural product should be revised.