摘要:

AbstractLong‐range chiral cooperativity in enantiomerically pure ferrocenylamine ligands containing both planar and multiple centers of chirality (multiple stereogenic C‐atoms) was demonstrated in the AuI‐catalyzed reaction of aldehydes and isocyanoesters. Synthetic methodology was developed for the synthesis of ferrocenylamine ligands with two and three chiral centers of known absolute configuration in the C‐side chain in addition to the planar chirality of the molecule. The diastereo‐ and enantioselectivity of the AuI‐catalyzed formation of thetrans‐ andcis‐dihydrooxazoles5and6, respectively, from benzaldehyde (1) and methyl isocyanoacetate (2) depend upon the sequence of chirality (absolute configuration of the chiral centers) in the side chain of the ferrocenylamine ligands. Particularly significant effects were observed upon the enantioselectivity for the minorcis‐dihydrooxazole6, for which, in certain cases, resulted in a change in the enantiomeric dihydrooxazole6produced in excess with a change in the absolute configuration of a distant chiral center. Significant effects upon diastereo‐ and enantioselectivity were observed when chiral ferrocenylamine ligands containing free OH groups were utilized. Using ligands containing a free OH group gave6with an absolute configuration opposite to that produced by the corresponding ester and carbamate derivatives. The possible mechanisms for the transmission of chiral information in the proposed stereoselective transition state (TS) was discussed, including both the formation of a stereogenic N‐atom and steric effects based up

ISSN:0018-019X    

DOI:10.1002/hlca.19910740502

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe chiral bicyclic imidazol derivatives7and8were obtained from D‐glucose derivative9by a sequence of selective protection/deprotection and intramolecularSN2 reactions. Triols7and8are analogues of 6‐epica‐stanospermine (4) and of 3,7a‐diepialexine (6), respectively, and are potential glycosidase inhibitors. However, their anti‐HIV activity proved to be only

ISSN:0018-019X    

DOI:10.1002/hlca.19910740503

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe absolute configurations of acetylated bretonin A (= (+}‐(R)‐1‐[(acetoxy)methyl]‐2‐{[(4E,6E,8E)‐dodeca‐4,6,8‐trienyl]oxy}ethyl4‐acetoxybenzoate; (−)‐1b) and isobretonin A (= (+)‐(S)‐3‐{[(4E,6E,8E)‐do‐deca‐4,6,8‐trienyl]oxy}‐2‐hydroxypropyl 4‐hydroxybenzoate; (+)‐2), previously isolated from an undetermined sponge of the North Brittany sea, were established by comparison with synthetic (+)‐lband (+)‐2, obtained from the condensation of commerical (−)‐(R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐ylp‐toluenesuifonate ((−)‐(R)‐15) with a mixture of (4E,6E,8E)‐ (14e) and (4E,6Z,8E)‐dodeca‐4,6,8‐trien‐1‐ol (14z). This also allowed confirming the structure and configuration of bretoninB(= (S)‐2‐{[(4E,6Z,8E)‐dodeca‐4,6,8‐trienyl]oxy}‐1‐(hydroxy‐methyl)ethyl 4‐hydroxybenzoate;3) which was also isolated from the same sponge, albeit in a too small amount for a complete study. As concerns the glyceryl ethers precursors of the bretonins, co‐occurrence of the usual (S)‐con

ISSN:0018-019X    

DOI:10.1002/hlca.19910740504

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of [Leu5]enkephalin‐related glycoconjugates with an ester‐, ether‐, or amide‐type linkage were synthesized and evaluated for antiviral activity against HIV‐1 in a cell‐culture system using peripheral blood lymphocytes. All tested glycoconjugates exhibited a certain antiviral activity which was significantly higher than the activity of the parent peptide compound itself. These results indicate that synthetic glycoconjugates of opioid peptides are good candidates for the development of anti

ISSN:0018-019X    

DOI:10.1002/hlca.19910740505

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractRaclopride, an antipsychotic 6‐methoxysalicylamide (= 2‐hydroxy‐6‐methoxybenzamide) derivative, was shown by titrimetry and UV‐pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate–ammonium ionic bond. These findings indicate that raciopride and other halogenated 6‐melhoxysalicylamides with a highly acidic phenolic group may not resemble otherortho‐methoxybenzamides in their stereoelectronic structure and mode of binding to the dopa

ISSN:0018-019X    

DOI:10.1002/hlca.19910740506

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractDevelopmental efforts to improve the yield of the chemical synthesis of (3R,3′R)‐zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by1H‐NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)‐isomers of zeaxanthin: (7Z)‐, (9Z), (13Z)‐, (15Z)‐, (7Z,7′Z)‐, (9Z,9′Z)‐ (7Z,9Z,7Z)‐, (7Z,11Z,7′Z)‐, (9Z,13Z,9′Z)‐, (7Z,9Z,7′Z,9′Z)‐, and (7Z,9Z,11Z,7′Z,9′Z)‐zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)‐, (7Z,7′Z)‐, (9

ISSN:0018-019X    

DOI:10.1002/hlca.19910740507

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe preparation of the optically pure tritertiary phosphine (RRR)‐MeSi(CH2P(t‐Bu)Ph)3 (2) is reported. The route followed involves deprotonation of optically pure (R)‐P(BH3)Me(t‐Bu)PH (2) the reaction of the resulting carbanion with MeSiCl3, followed by removal with morpholine of the BH3‐protecting groups from the triertiary phosphine‐borane3. The latter's X‐ray crystal structure and that of [Rh(NBD)((RRR)‐1]TOf)(4), are also rported. Furthermore, it is shown that the separation of the racemic phosphine‐borane2can be conveniently carried out using medium‐pressure liquid chromatgrapy with cellulose‐riacetate as a ch

ISSN:0018-019X    

DOI:10.1002/hlca.19910740508

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe cluster compounds [Pt3(μ‐CO)3(PR3)3] act asLewisbases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ‐CO)3(PR3)3}]. The X‐ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ‐CO)3(PPh(

ISSN:0018-019X    

DOI:10.1002/hlca.19910740509

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe stereo and face selectivities of the cycloaddition of 1,2,3‐trichloro‐3‐fluorocyclopropene (1a) with acyclic dienes and furans has been re‐investigated by X‐ray determination and correlation of19F‐NMR data. The isolated adducts of dienes exclusively haveexo‐configuration, andexo‐Configuration predominates with furans. The Cl substituents of the resulting cyclopropane ring arecis‐oriented. The face selectivity of the reaction with both types of substrates is attributed to electrostatic interactions between the F and the bridgehead Cl substituents, which destabilize the F‐cis‐transition state (13(F

ISSN:0018-019X    

DOI:10.1002/hlca.19910740510

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

Ring Enlargement of 1,2‐Thiazol‐3(2H)‐one‐1,1‐dioxides and 3‐Amino‐2H‐azirines to 4H‐1,2,5‐Thiadiazocin‐6‐one‐1,1‐dioxidesReaction of 3‐amino‐2H‐azirines2with the 1,1‐dioxides4and7of 1,2‐thiazol‐3(2H)‐ones and 1,2‐thiazoli‐din‐3‐ones, respectively, in i‐PrOH at room temperature leads to 4H‐1,2,5‐thiadiazocin‐6(5H)‐one‐1,1‐dioxides5(Scheme 2, Table) and the corresponding 7,8‐dihydro derivatives8(Scheme 4), respectively. The structure of some of the new 8‐membered heterocycles as well as the structure of the minor by‐product6(Scheme 3) have been established by X‐ray crystallography (Chapt. 4). The proposed reaction mechanism for the ring expansion to5and8(Scheme 2) is in accordance with previously published results of reactions of2and NH‐acidic heterocycles and is further supported by

ISSN:0018-019X    

DOI:10.1002/hlca.19910740511

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY