摘要:

AbstractA novel macrocyclic tetrapyrrolelactam8, analog of a putative intermediate, has been synthesized. Its very low inhibitory effect on Uro'gen III synthase renders it unlikely to be a low‐energy transition‐state ana

ISSN:0165-0513    

DOI:10.1002/recl.19961150102

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractStudies of the dichloromethane extract of stems and the methanolic extract of fruits ofPiper wightiiMiq. resulted in the isolation of 12 compounds, all new for this species. They comprise a novel neolignan1, a neolignan new as a natural product2, a novel cyclohexane5, two known neolignans3and4, one known cyclohexane6, and six known alkaloids7, 8, 9, 10, 11and12.

ISSN:0165-0513    

DOI:10.1002/recl.19961150103

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe reaction rate and stereoselectivity of intermolecular dipolar 1,3 cycloaddition of theC,N‐dialkylnitrone to olefins with hydroxyl groups and their derivatives were found to depend upon the type of hydroxyl group. The rate is accelerated in the order: magnesium alkoxide (OMgBr); free hydroxyl group (OH); ether (OR). Selectivities are improved moderately when magnesium alkoxide is use

ISSN:0165-0513    

DOI:10.1002/recl.19961150104

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe synthesis of (R)‐ and (S)‐2‐hydroxy‐3‐enoic acid esters [(R)‐1a‐dand (S)‐1a‐c] is described. The (R) enantiomers were prepared by a Pinner synthesis from the corresponding (R)‐cyanohydrins [(R)‐2a‐d], which in turn were obtained by R‐oxynitrilase‐ (E.C. 4.1.2.10)‐catalyzed addition of HCN to the α,β‐unsaturated aldehydes3a‐d. For the preparation of the (S) enantiomers an inversion of the configuration had to be implemented. A critical evaluation of the two possible sequences: inversion of the configuration of the cyanohydrins followed by solvolysis of the nitrile function, and solvolysis of the cyanohydrins followed by inversion of the configuration of the resulting α‐hydroxy esters, c

ISSN:0165-0513    

DOI:10.1002/recl.19961150105

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19961150106

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe reactions between isatin (8a) andN‐acetylisatin (8b) with pyridine‐2,3‐diamine (9a), pyridine‐3,4‐diamine (9b) and pyrimidine‐4,5‐diamine (21) were studied. 10H‐Pyrido[3′,2′:5,6]pyrazino[2,3‐b]indole (5a), 6H‐pyrido[2′,3′:5,6]‐pyrazino[2,3‐b]indole (5b), 6H‐pyrido[3′,4′:5,6]pyrazino[2,3‐b]indole (5c) and 10H‐pyrido[4′,3′:5,6]pyrazino[2,3‐b]indole (5d) were regioselectively synthesized in a three‐step synthesis fromN‐acetylisatin and the appropriate pyridine diamine. The structures of the intermediates were assigned by NOESY experiments. In the same manner, 10H‐indolo[3,2‐g]pteridine (24) was sy

ISSN:0165-0513    

DOI:10.1002/recl.19961150107

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper describes a study of the effects of chain flexibility and chain packing on the properties of vesicles formed from sodium di‐n‐alkyl phosphates. Three di‐n‐alkyl phosphates with a constant chain length but with different degrees of unsaturation have been synthesized: dioleyl phosphate (DOP) and dielaidyl phosphate (DEP) having, respectively, acisand atransdouble bond at C‐9 and the saturated distearyl phosphate (DSP). These surfactants form vesicles, as confirmed by transmission electron microscopy (EM). The gel to liquid‐crystalline phase transition was studied using both fluorescence polarization and differential scanning microcalorimetry. According to fluorescence polarization, using trans, trans, trans‐1,6‐diphenyl‐hexa‐1,3,5‐triene (DPH) as a probe, DSP vesicles undergo a cooperative transition from a gel to a liquid‐crystalline state at 72°C. The polarization of the probe captured in DOP or DEP vesicles decreased gradually in the temperature range 0–40°C, indicating a non‐cooperative phase transition. It appears that the vesicle bilayer is in a gel state below 0°C and in a liquid‐crystalline state above 40°C. A temperature‐dependent31P NMR study failed to identify the exact phase‐transition temperature. The effect of the fusogenic cation Ca2+was studied qualitatively using EM. Calcium induces fusion of DEP vesicles but, within a short time, tubules are formed which are most probably anhydrous crystals of the calcium salts. For DSP vesicles the latter process is extremely fast and fused vesicles cannot be detected. In contrast, DOP vesicles fuse under the influence of calcium, but no crystallization takes place. The fused DOP vesicles are stable for more than one week in the presence of 4 mM Ca2+stored at room temperature or at 60°C. Addition of EDTA to DOP vesicles leads to chelation of the calcium ions and to

ISSN:0165-0513    

DOI:10.1002/recl.19961150108

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn a study of the development of a strong inhibitor for γ‐glutamyl transpeptidase (γ‐GTP), the inhibitory effect of 21 arylboronic acids was determined in the γ‐GTP‐mediated hydrolysis ofN‐(L‐γ‐glutamyl)‐4‐nitroanilide. It was shown that most boronic acids can moderately inhibit the enzyme activity and, in particular, the inhibitory effects of (3‐formylphenyl)boronic acid and (3‐carboxyphenyl)boronic acid (9% and 12%, respectively) are comparable to that reported for the binary L‐serine‐plus‐borate inhibition system (7%). Furthermore, it was shown that the addition of physiologically nontoxic saccharides is very effective in regenerating the enzyme activity. This effect is attributed to the competitive binding of saccharides with the boronic acid inhibitor to pull it out into the water phase. Thus, this paper offers a novel methodology for inhibitio

ISSN:0165-0513    

DOI:10.1002/recl.19961150109

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractEphedrine can be readily converted by means of intramolecular SN2 substitution by the hydroxyl or amino substituent into, respectively, the corresponding epoxide or aziridine with high stereocontrol. Subsequent stereoselective ring opening at the benzylic centre using tetrabutyl‐ammonium fluoride (TBAF) and dithiols affords theC2symmetrical hydroxy or amino sulfides in excellent yield. Application of these ligands in a palladium‐catalyzed asymmetric allylic substitution reaction gave moderate to high enantiomeric excesses (up to 79%) and high yields of prod

ISSN:0165-0513    

DOI:10.1002/recl.19961150110

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThree consecutive reactions are observed when the phosphate triester6is hydrolysed. At pH<7 rapid cyclisation gives the triester12, with the loss of the hemiacetal leaving group (3,4‐dichlorophenoxy)methanol (which rapidly breaks down to the phenol). The effective molarity of the neighbouring OH group is of the order of 1012M.12is then hydrolysed by C‐O cleavage to give the diester11. In base, the first two reactions are complete almost instantaneously, and the final phosphorus‐containing products are (3,4‐dichlorophenoxy)methyl methyl phosphate diester, and the methyl phosphate dianion. These must come from C‐O cleavage reactions of diester14and the rearranged benzylic triester15, which rapidly eliminate phosphate ester leaving groups to give the same quinon

ISSN:0165-0513    

DOI:10.1002/recl.19961150111

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY