Showing papers on "Total synthesis published in 1987"

Plant antitumor agents. 28. Resolution of a key tricyclic synthon, 5'(RS)-1,5-dioxo-5'-hydroxy-2'H,5'H,6'H-6'-oxopyrano[3',4'-f].DELTA.6,8-tetrahydroindolizine: total synthesis and antitumor activity of 20(S)- and 20(R)-camptothecin

Abstract: The resolution of the tricyclic ketone (3a + 3b) by the separation of diastereomeric adducts 4a and 4c of the precursor ketal 5 is described. The regenerated enantiomers 3a and 3b of 100% optical purity represent the key intermediates from which 20(R)-camptothecin (1a) and 20(S)-camptothecin (1b), respectively, have been prepared. The 20R analogue 1a was 10-100 times less active than the natural 20(S)-camptothecin (1b) in 9KB and 9PS cytotoxicity assays and almost inactive in in vivo L-1210 leukemia tests as compared to the highly potent and active natural compound 1b.

Total synthesis of (.+-.)-15-deoxyspergualin

Abstract: Synthese a partir de spermidine protegee et de (N 1 ,N 2 -di-t-butoxycarbonyl S-methyl) thiocarbamimidate

Concise total synthesis of (+)-(9S)-dihydroerythronolide A

Abstract: The triol (I), whose synthesis via the butenolide template method is reported in the preceding paper, is used as starting material for the synthesis of the title compound (VII).

A versatile and efficient synthesis of carbinolamine-containing pyrrolo[1,4]benzodiazepines via the cyclization of N-(2-aminobenzoyl)pyrrolidine-2-carboxaldehyde diethyl thioacetals: total synthesis of prothracarcin

Abstract: A versatile and efficient synthesis of carbinolamine-containing pyrrolo[1,4]benzodiazepines (or the corresponding imine forms) of types 2, 7, and 8 is described that involves mercuric chloride mediated cyclization of the corresponding N-(2-aminobenzoyl)pyrrolidine-2-carboxaldehyde diethyl thioacetals. This new synthesis has significant advantages over previously existing methods in that (a) catalytic hydrogenation is not involved in the cyclization process, thus allowing preservation of unsaturation in the product, (b) all steps are mild and take place in high yields, (c) the success of the reaction is apparently independent of substituent effects, (d) the reaction proceeds with retention of stereochemistry at the aldehyde-bearing carbon, and (e) it can be readily adapted for the convergent synthesis of a variety of analogues. In addition to the synthesis of some model carbinolamine-containing compounds, the overall utility of this procedure is demonstrated by the total synthesis of prothracarcin (2d), a natural product with antitumor activity from Streptomyces umbrosus. This allowed confirmation of the E configuration previously assigned to the C2-ethylidene side chain of prothracarcin.

Total synthesis of (.+-.)-atractyligenin

Abstract: Synthese a partir du methyl-2 cyclohexadiene-1,4 ethanol via un tricycloocteno par cyclopropanation, cyclisation et fonctionnalisation

Regio- and stereoselectivity of the reaction between cyanocuprates and cyclopentene epoxides. Application to the total synthesis of prostaglandins

Abstract: Synthese de PGE1, decarboxy-2 hydroxymethyl-2 PGE1, PGF1α, PGF2α a partir de l'alkyl-4oxa-6bicyclo [310] hexanol-1 Ce dernier represente l'un des composes obtenus par l'addition de cyanocuprates de lithium du type Li(RCuCn) ou R=alkyl, vinyl, phenyl sur l'oxa-6bicyclo [310] hexene-2

Total synthesis of 7,7-, 10,10-, and 13,13-difluoroarachidonic acids

Abstract: Synthese a partir de la reaction d'(alcynyl trialkylsilyl) ethers avec le ([difluoro-4,4 iodo-4 butyne-2 yl] [perhydro pyrannyl-2]) ether en presence de butyl-lithium

A convergent general synthetic protocol for construction of spirocyclic ketal ionophores: an application to the total synthesis of (-)-A-23187 (calcimycin)

Abstract: Synthese de t-butyldiphenylsiloxy-2″ ethyl-6' [hydroxymethyl-1' ethyl]-6 perhydro trimethyl-3,5,5' spirobi-2:2'-pyrane via la reaction du dihydro-3,4 methoxymethoxymethyl-1' ethyl-2 methyl-3 pyranne avec le bromo-1 t-butyldimethylsiloxy-4 t-butyldiphenylsiloxy-6 methyl-3 hexane. Application a la synthese de la calcimycine

Preparation of acyltetronic acids using t-butyl acetothioacetate: total synthesis of the fungal metabolites carolic, carlosic, and carlic acids

Abstract: Dianions generated from S-t-butyl acetothioacetate (1) were alkylated with a variety of electrophiles at the γ-carbon centre. Treatment of the alkylated products with 2-hydroxy esters in the presence of silver(I) salts gave transesterified acetoacetate derivatives in good yields. These acetoacetates were cyclised efficiently to acyltetronic acid derivatives using tetrabutyl ammonium fluoride in THF solution at room temperature. By an appropriate choice of substituents the total syntheses of the fungal metabolite natural products carlosic, carolic, and carlic acids have been achieved.