Helvetica Chimica Acta

doi: 10.1002/hlca.19910740501pmid: N/A

Pastor, Stephen D.; Togni, Antonio

doi: 10.1002/hlca.19910740502pmid: N/A

Long‐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 the trans‐ and cis‐dihydrooxazoles 5 and 6, 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 minor cis‐dihydrooxazole 6, for which, in certain cases, resulted in a change in the enantiomeric dihydrooxazole 6 produced 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 gave 6 with 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 upon Newman's rule of six.

Frankowski, Andrzej; Seliga, Czeslawa; Bur, Daniel; Streith, Jacques

doi: 10.1002/hlca.19910740503pmid: N/A

The chiral bicyclic imidazol derivatives 7 and 8 were obtained from D‐glucose derivative 9 by a sequence of selective protection/deprotection and intramolecular SN2 reactions. Triols 7 and 8 are 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 marginal.

Mancini, Ines; Guella, Graziano; Pietra, Francesco

doi: 10.1002/hlca.19910740504pmid: N/A

The absolute configurations of acetylated bretonin A (= (+}‐(R)‐1‐[(acetoxy)methyl]‐2‐{[(4E,6E,8E)‐dodeca‐4,6,8‐trienyl]oxy}ethyl 4‐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 (+)‐lb and (+)‐2, obtained from the condensation of commerical (−)‐(R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐yl p‐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 bretonin B (= (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‐figuration (from 1a) with the unusual (R)‐configuration (from (+)‐2)) poses intriguing biogenetic problems.

Horvat, Štefica; Varga, Lidija; Horvat, Jaroslav; Pfützner, Andreas; Suhartono, Haryadi; Rübsamen‐Waigmann, Helga

doi: 10.1002/hlca.19910740505pmid: N/A

A 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‐HIV agents.

Carrupt, Pierre‐Alain; Tsai, Ruey‐Shiuan; Tayar, Nabil El; Testa, Bernard; de Paulis, Tomas; Högberg, Thomas

doi: 10.1002/hlca.19910740506pmid: N/A

Raclopride, 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 other ortho‐methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D2 receptor.

Englert, Gerhard; Noack, Klaus; Broger, Emil A.; Glinz, Ernst; Vecchi, Max; Zell, Reinhard

doi: 10.1002/hlca.19910740507pmid: N/A

Developmental 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 by 1H‐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)‐, (9Z,9′Z)‐, (7Z,9Z,7′Z)‐, and (7Z,9Z,7′Z‐9Z)‐isomers.

Ward, Thomas R.; Venanzi, Luigi M.; Albinati, Alberto; Lianza, Francesca; Gerfin, Tobias; Gramlich, Volker; Tombo, Gerardo M. Ramos

doi: 10.1002/hlca.19910740508pmid: N/A

The 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‐borane 3. 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‐borane 2 can be conveniently carried out using medium‐pressure liquid chromatgrapy with cellulose‐riacetate as a chiral stationary phase.

Stockhammer, Andreas; Dahmen, Klaus‐Hermann; Gerfin, Tobias; Venanzi, Luigi M.; Gramlich, Volker; Fetter, Walter

doi: 10.1002/hlca.19910740509pmid: N/A

The cluster compounds [Pt3(μ‐CO)3(PR3)3] act as Lewis bases 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(i‐Pr)2)3}].

Müller, Paul; Bernardinelli, Gérald; Pfyffer, Jean; Schaller, Jean‐Pierre

doi: 10.1002/hlca.19910740510pmid: N/A

The 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 of 19F‐NMR data. The isolated adducts of dienes exclusively have exo‐configuration, and exo‐Configuration predominates with furans. The Cl substituents of the resulting cyclopropane ring are cis‐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‐cis)) over 13 (F‐trans).