Dibenzylbutyrolactone Lignans and Coumarins from Ipomoea cairica *

From the aerial parts of Ipomoea cairica (L.) Sweet (Convolvulaceae) the coumarins umbelliferone and scopoletin, and the dibenzyl-γ-butyrolactone lignans arctigenin, matairesinol and trachelogenin, were iso lated along with β-sitoterol and fatty ac ids. The anal y sis of the RMN C spec tra of these and other lignoids de scribed in the lit er a ture made it pos si ble to re vise some chem i cal shift as sign ments.


Re sults and Dis cus sion
The aque ous meth a nol ex tract of a spec i men of Ipomoea cairica was ex tracted suc ces sively with chlo ro form and n-butanol.The sep a ra tion of lignoids 1-3 and coumarins 4 and 5 was achieved by chro ma tog ra phy on an alu mina col umn and sil ica gel pre para tive thin layer chro ma tog ra phy of the chlo ro form ex tract.Com pounds 1-5 have been pre vi ously reported.Lignoid 1 has been iso lated from Arctium lappa (Compositae) 5 , For sythia xoreana, and F. viridissima (Oleaceae) 2 , 2 from Stellera chamaejasme (Thymelaeaceae), Tsuga chinensis (Pinaceae), F. xorena, and F. viridissima (Oleaceae) 2 , and 3 from Trachelospermum asiaticum (Apocynaceae) 6 .Coumarins umbelliferone (4) and scopoletin (5) have been re corded in sev eral spe cies of the Convolvulaceae fam ily.Scopoletin ap pears in Ipomoea batatas as a phytoalexin 7,8 .
Dur ing the course of our anal y sis of the 13 C-NMR spec tra of com pound 1 and the mix ture of 2 and 3 it was noted that some chem i cal shift as sign ments re cently pub lished for these and other lignoids 9,10 re quired re vi sion (Ta ble 1).
As an tic i pated, the com par i son of the chem i cal shifts of the car bon at oms of lignoid 7 with those of the 9'-oxo compound (e.g. 6) clearly showed a γ-ef fect at C-7' due to the intro duc tion of the car bonyl ox y gen at C-9' (Ta ble 1).Thus, some as sign ments have been re vised for the non-aromatic car bon at oms of com pounds 6 9 and 8 10 (Ta ble 1).The chem ical shifts for the ar o matic car bon C-5 (methine ortho to the methoxyl group) and C-5' (methine ortho to the hydroxyl group) in lignoids 1 and 3 were dis tin guished on the ba sis of the γ-ef fect of the methyl of the 3-OMe group ( e.g.9-11 ) 11 .Model com pounds 9-11 may also be used to dem on strate the known shield ing ef fects in duced by OH and OMe groups in the para and ortho po si tions, and the deshielding ef fect on the ipso -car bon by methylation.The ox y gen atom of the hydroxyl group at C-8' is re spon si ble for an up field shift of the C-1' and C-7 ( γ-ef fect).

Con clu sions
Convolvulaceae is a large fam ily com pris ing about 59 gen era and more than 1800 spe cies, which are found in trop ical and sub trop i cal re gions as herbs, climb ers, or shrubs 12 .The nat u ral prod ucts re ported in the spe cies of this fam ily may be clas si fied as polyketides, terpenoids (mono-, sesqui-, di-, and triterpenoids), ste roids, shikimides (coumarins and ben -zoic and cinnamic acid de riv a tives), flavonoids (flavonols, anthocyanins, fla vones, flavanones), one xanthone (mangiferin), al ka loids (pyrrolidines, tropanes, indolizidines, and ergolines), and other com pounds.To the best of our knowl edge, lignoids such as 1-3 have been hith erto un reported as nat u ral prod ucts of the Convolvulaceae fam ily, with the ex cep tion of pinoresinol dimethyl ether ( 12 ) which has been iso lated from Humbertia madagascariensis 3 .The fact that umbelliferone ( 4) was iso lated points to the pos si bil ity that the spec i men used in our in ves ti ga tion had been in fested by a fun gus, since this sub stance was re cently found to be a phytoalexin in I. batatas 7,8 .More over, it can be as sumed that lignoids were also biosynthesized as phytoalexins.At the ecolog i cal level, there is ev i dence that lignans play a role in plant-plant, plant-fungus, and plant-insect in ter ac tions 13 .Matairesinol ( 2), formed via the cou pling of two phenylpropane units hav ing the ferulic sub sti tu tion pat tern, would be a log i cal pre cur sor of the other lignoids 1 and 3 through methylation of the hydroxyl group lo cal ized at C-4' 14 .
Ta ble 1. 13 C NMR spec tral data for Lignoids 1-3 iso lated from Ipomoea cairica com pared with 6, 7 9  b Values given in pa ren the ses are the re ported chem i cal shifts of cor re spond ing com pounds a s de scribed in the lit er a ture 9,10 .
Phytochemical stud ies of other spec i mens of Ipomoea cairica have also re vealed the pres ence of the lignanolides arctigenin 1 and trachelogenin 3 in an aque ous meth a nol ex tract 15 .That in ves ti ga tion was prob a bly de vel oped during the same pe riod as our study of the same spe cies.

Gen eral
Mps are un cor rected.NMR ( 1 H: 100 and 200 MHz; 13 C: 25.2 and 50.3 MHz) spec tra were re corded in a CDCl 3 so lu tion with TMS as the in ter nal stan dard.EIMS were mea sured by di rect in let at 70 eV ion iza tion.GC/MS spectra were mea sured on a GCHR/MS-C 5987A (HP) spectrom e ter, us ing a cap il lary glass col umn (OV-1701; 20 m).

Plant ma te rial
The plant ma te rial of Ipomoea cairica (L.) Sweet, Convolvulaceae fam ily, was col lected on the cam pus of the Universidade Fed eral do Rio de Ja neiro, Rio de Ja neiro, Brazil.The spec i men was iden ti fied by Rosa Fuks, Jardim Botânico do Rio de Ja neiro (voucher spec i men nº 257337), Rio de Ja neiro, Brazil.

Iso la tion of the con stit u ents
Dried and milled whole plant (1.35 kg) was ex tracted at room tem per a ture with hex ane and then with MeOH.A por tion (1 g) of the res i due ob tained from the hex ane extract (98 g) was dis solved in ether and treated with aque ous 10% NaHCO 3. Af ter neu tral iza tion and ex trac tion with ether, the aque ous so lu tion gave a mix ture of fatty ac ids (60 mg).The re main ing res i due (97 g) was dis solved in hex ane and fil tered on a CaCO 3 col umn to elim i nate chlo ro phyll.The hex ane so lu tion was concd. in vacuo and the res i due was sub mit ted to sil ica gel col umn chro ma tog ra phy.Elution with hex ane and hex ane-EtOAc (9:1) gave aliphatic ma te rial and β-sitosterol, re spec tively.

Iden ti fi ca tion
The known com pounds 1 5 , 2, 3 2 , 4 15 , and 5 16 were identi fied by com par i son with au then tic sam ples ( 2-5 ) and by spec tral data, in clud ing de riv a tives ob tained by acetylation (1a ) with Ac 2 O/Py and methylation ( 2a ) with CH 2 N 2 /ether.The fatty ac ids mix ture was meth yl ated with CH 2 N 2 /ether, and the methyl es ters of palmitic and stearic ac ids were iden ti fied by GC/MS.

Ac knowl edg ments
This study was sup ported by a re search fel low ship and by grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), the Financiadora de Estudos e Projetos (FINEP), and the Coordenação de Aperfeiçoamento de Pessoal de Ensino Su pe rior (CAPES).The au thors are grate ful to Pro fes sors Antônio J.R. da Silva (NPPN, Universidade Fed eral do Rio de Ja neiro) for the NMR spec tra ( 1 H: 100 MHz; 13 C: 25.2 MHz) and MS spectra, Jary Nóbrega (Instituto de Química, Universidade Federal do Rio de Ja neiro) for pro vid ing the GC/MS, Sansei Nishibe (De part ment of Pharmacognosy, School of Pharma ceu ti cal Sci ences, Ja pan) for sam ples of com pounds 2 and 3, Vic tor Rumjanek (Departamento de Química, Universidade Fed eral Ru ral do Rio de Ja neiro) for NMR ( 1 H: 200 MHz) spec tra, and Ceres M.R. Gomes (Departamento de Química, Universidade Fed eral Ru ral do Rio de Ja neiro) for the in ter est and use ful sug ges tions in the con clu sion of the M. Sc. the sis.
* The spec tra were re corded in CDCl 3 ( 1 -3 , 6, and 8) and D 2O + CD 3COCD 3 ( 7), chem i cal shifts on the δ (ppm) scale with TMS as int.stan dard; a Sig nals with same let ter may be in ter change able in each ver ti cal col umn.