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â-Phenylethylamines and the isoquinoline alkaloids Kenneth W. Bentley Marrview, Tillybirloch, Midmar, Aberdeenshire, UK AB51 7PS Covering: July 1996 to June 1997 and cobalt salts have been prepared, the copper derivatives Previous review: 1997, 14, 387 being much the most stable.6 Highly diastereoselective additions of lithium alkyls to the 1 â-Phenylethylamines (2S)-aziridine aldehyde 3 have been achieved, as a result of 2 Isoquinolines chelation-controlled carbon–carbon bond formation, to give 3 Naphthylisoquinolines the alcohols 4, which have been catalytically reduced selec- 4 Benzylisoquinolines tively to 5, relatives of ephedrine and pseudoephedrine. Similar 5 Bisbenzylisoquinolines reactions have been accomplished with the R isomer of 3.7 6 Cularines 7 Pavines and isopavines 8 Berberines and tetrahydroberberines Ph Ph 9 Secoberberines Ph MeC HMe C H 10 Protopines OH MeC H OH NN H 11 Phthalide-isoquinolines HN 12 Spirobenzylisoquinolines CHO R R H 13 Indanobenzazepines HHMe H 14 Rhoeadines 34 5 15 Other modified berberines 16 Emetine and related alkaloids 17 Benzophenanthridines The pharmacological and physiological effects of ephe- 18 Aporphinoid alkaloids 8,9,10 10 11 drine, of methylephedrine and of pseudoephedrine 18.1 Proaporphines have been studied. 18.2 Aporphines 18.3 Dimeric aporphines 18.4 Benzylisoquinoline–aporphine dimers 18.5 Phenanthrenes 2 Isoquinolines 18.6 Oxoaporphines The new alkaloids stephaoxocanine 6 and stephaoxocanidine 7 18.7 Dioxoaporphines have been isolated from Stephania cepharantha.1,12 These are 18.8 Aristolochic acids and aristolactams analogues of excentricine, reported in the previous review, and 19 Alkaloids of the morphine group 20 Phenethylisoquinolines 21 Colchicine MeO MeO MeO 22 Erythrina alkaloids 22.1 Erythrina alkaloids N NH NR MeO MeO MeO 22.2 Cephalotaxine and related alkaloids H HHH H OH 23 Other isoquinolines O O O 24 References 1 â-Phenylethylamines OH OH OH trans-N-Feruloyltyramine has been isolated from Stephania 678a R = H cepharantha.1 The yields of ephedrine and dihydropseudo- 8b R = Me MeO ephedrine from plants derived from axillary buds of Ephedra gerardiana and from the parent plants have been N compared.2 HO Ephedrine and pseudoephedrine have been condensed with Me paraformaldehyde to give the oxazolines 1a and 1b, respect- 9 ively,3 and the oxazolines 2a, 2b and 2c have been prepared a comparison of the spectra of these three alkaloids has 12 1 Ph suggested a reversal of the absolute stereochemistry of R O O 2 excentricine from that given in the previous review to 8a. R CH2 R Methylexcentricine, 8b on this basis, has been isolated as N N 13 Me Me Me Me a new alkaloid from Stephania excentrica. 7-O- 1 2 1a R = Ph; R = H 2a R = CHMe2 Demethylisosalsolidine 9 has been isolated as a new alkaloid 1b R1 = H; R2 = Ph 2b R = Ph from Hernandia nymphaeifolia.14 N-Cyanomethylsalsoline has 2c R = p-Anisyl been prepared.5 A convenient process for the synthesis of (&)-carnegine from N-methylhomoveratrylamine and acetic acid, by from pseudoephedrine.4 N-Cyanomethylephedrine and Bischler–Napieralsky cyclisation with polyphosphoric acid and N-cyanomethylpseudoephedrine have been prepared.5 Com- subsequent reduction with sodium borohydride, has been plexes of ephedrine and of norephedrine with copper, nickel described.15 A stereospecific synthesis of (R)-salsolidine 10 has Bentley: â-Phenylethylamines and the isoquinoline alkaloids 341 Me OMe OMe MeO Me Me MgBr N MeO Me NH Zn Et MeO O S Me Ph NH 10 11 OMe N OMe Me Pri OMe OMe 17 18 OMe OMe MeO MeO O R Me MeO Me N NMe MeO MeO N O Ph2PO O 12 13 OMe Me 19a R = CONH2 19b R = Me been achieved by the catalytic reduction of 1-methyl-6,7- dimethoxy-3,4-dihydroisoquinoline using the chiral zinc com- 16 plex 11 as catalyst. The benzophenone amide 12 has been O-methylancistocladine 19b.20 The boronic acid derivative 20a cyclised to the 4-aryltetrahydroisoquinolone 13 by potassium has been condensed with the iodides 21a and 21b to give, after hexamethyldisilazide, and the product has been reduced with reduction and removal of the benzyl groups from oxygen and 17 lithium aluminium hydride to (&)-O-methylcherylline. nitrogen, ancistrobrevine B and korupensamine C.21 In a similar manner korupensamine D has been prepared from 20b and 22.22 The bromo compound 23 has been coupled with the 3 Naphthylisoquinolines Five new naphthylisoquinoline alkaloids have been isolated from the following plant species: Ph OMe OR Ancistrocladus tectorius18 I 6-O-methyl-8-O-demethylancistrocladinine 14a,6-O- O Me methyl-4*-O-demethylancistrocladinine 14b and 6-O- N methyl-8,4*-O-demethylancistrocladinine 14c Me Ancistrocladus korupensis19 B(OH)2 ORMe Ph yaoudamine A 16 and its 6-rhamnoside (yaoudamine B). 20a R = Me 21a R = Me 20b R = H 21b R = CH2Ph Ph Ph Br OMe OR1 OMe OR I O Me O Me N N Me Me PhO Me Ph PhO Me Ph MeO Me MeO Me 22 23 N NH OMe OPri OR2 Me OMe 14a R1 = Me; R2 = H 15a R = Me 14b R1 = H; R2 = Me 15b R = H Me 1 2 14c R = R = H SnBu3 24 HO Me N organotin derivative 24 to give O-benzylkorupensamines A OMe Me and B, which have been oxidised by silver oxide and de- HO benzylated to give a mixture of michellamines A, B and C.23 Palladium-catalysed cross coupling of tetrabenzyl- MeO Me korupensamine A 6*-boronic acid with 6*-bromotetra- 16 benzylkorupensamine B, followed by removal of the benzyl groups, has afforded michellamine B only.24 A patent has been published covering previously described syntheses of the Spectroscopic studies suggest that the free bases 14a and 14c michellamines, directly and from the korupensamines.25 exist in the tautomeric keto forms 15a and 15b. The absolute Interest in the antiviral properties of the michellamines has stereochemistry of these alkaloids at C-3 has been deduced led to the synthesis of analogues of these alkaloids. 4,4*- from their CD spectra and confirmed by the oxidation of 14c Didemethoxy-2,2*-didemethylmichellamine B 25, synthesised to (3S)-aminobutyric acid.18 by processes analogous to the previously reported direct The Grignard reagent 18 has been condensed with the synthesis of michellamine, inhibits recombinant HIV reverse dihydrooxazole 17 and the product has been hydrolysed to transcriptase at 60 ìgml"1.26 The naphthyltin derivative 24 the amide 19a, which was separated into its atropomers in the has been converted into 26a, and oxidation of the related ratio 6:1, the major component of which was converted into phenol 26b gave a dimeric quinone, which was reduced to 342 Natural Product Reports, 1998 Me OH Dioncophylline A and some of its 8-ethers, especially the 8-O-benzyl and 8-O-(4-bromobenzyl) derivatives, show growth HN retardant activity against larvae of Spodoptera littoralis; OR OMe studies of other derivatives shows that a free NH group is Me OH essential for this activity.30 OH Me 4 Benzylisoquinolines OH Benzylisoquinoline alkaloids have been isolated from the MeO following plant species, the six marked with asterisks being HO Me new alkaloids: 31,32 Me N Me Berber turcomanica NH papaverine and turcomanine* 30 33 Ph Papaver setigerum 25 OH Me 26a R = Pri laudanosine, papaverine, setigerine* 31a and setigeridine* 26b R = H 31b H Me N Me OMe MeO MeO N N Me HO MeO OH OMe OR1 OH MeO 2 OMe OH OH OR Me 30 31a R1 = R2 = Me 1 2 31a R R = CH2 MeO MeO Cl– + NMe2 NMe2 MeO MeO Me N Me H H R OH OH 27 OMe OMe 32a R = H 33 pindikamine A 27, with an unnatural ‘skew’ structure. This 32b R = OMe shows no antiviral activity, but is active against Plasmodium falciparum at 1.23 ìgml"1, compared with 3.49 ìgml"1 for the monomer 26b.27 Dioncophylline A 28a has been bromi- nated to 28b, the benzyl ether of which was dimerised by Polyalthia insignis34 tert-butyllithium at low temperature to a single rotamer of polysignine* 32a and methoxypolysignine* 32b jozimine A 29, which equilibrated to a mixture at room Stephania cepharantha1,35 "1 temperature. This was found to be active at 0.75 ìgml coclaurine, N-methylcoclaurine, juziphine, norjuziphine, against the asexual erythrocytic stage of Plasmodium laudanidine, protosinomenine and reticuline falciparum; the monomer 28a is active against the same Stephania excentrica36 coclaurine and N-methylcoclaurine Zanthoxylum nitidum37 OMe isotembetarine chloride* 33. The crystal structure of papaverine38 and the 15N NMR OMe 39 Me OH spectrum of armepavine have been studied. N-Chloro- acetylnorlaudanosine methine 34, on photolysis in the presence 40 HN of oxygen, has given the cyclised lactams 35 and 36. Me The condensation of -gluconolactone with homovera- R Me trylamine has yielded the amide 37, which was cyclised, Me Me N-methylated and reduced to 38a. Oxidation of this to Me Me the aldehyde 38b, followed by treatment with 3,4- NH NH dimethoxyphenyllithium, afforded hydroxy-(R)-laudanosine 39a, which was hydrogenolysed to give (R)-(")-laudanosine OH Me 41 MeO OH Me 39b. (S)-(")-Norlaudanosine has been synthesised in MeO good enantiomeric yield by the hydrogenation of 1-(3,4- MeO MeO dimethoxybenzyl)-6,7-dimethoxy-3,4-dihydroisoquinoline in 28a R = H 29 the presence of chiral iridium complexes,42 and stereoselective 28b R = Br reduction of the corresponding 1-(3-hydroxybenzyl) com- pound has given (R)-noranicanine.43Bischler–Napieralsky cyclisation of the amide 40, followed by reduction of the organism at 1.44 ìgml"1.28 Antimalarial activity has also resulting chiral iminium salt and N-methylation, has afforded been found in 7-epidioncophylline A, 5*-O-demethyl-6-O- the benzylisoquinoline 41,44 which differs from the alkaloid methyl-7-epidioncophylline A, dioncolactone A and dionco- fumarizine, to which this structure has been assigned.45 phylline C, the last being the most active of the whole group The Reissert compound 42 on treatment with 2-benzyloxy- "1 29 with IC50=0.014 ìgml .