Studies on the alkaloids of Solanum of northeastern Brazil

ARTIGO

Studies on the alkaloids of Solanum of northeastern Brazil

Tania M. Sarmento Silva; Maria de Fátima Agra; Jnanabrata Bhattacharyya^*

Laboratório de Tecnologia Farmacêutica, Universidade Federal da Paraíba, C.P. 5009, 58051-970, João Pessoa, PB, Brazil

ABSTRACT

In our continued studies on the genus Solanum for detecting a good source of soladodine, the steroid alkaloid potentially important for the manufacture of steroid hormones, as well as other compounds of potential therapeutic value, we investigated the fruits of Solanum crinitum, S. rhytidoandrum, and S. jabrense belonging to the subgenus Leptostemonum and S. stipulaceum, belonging to the subgenus Brevantherum, allof which are native of the northeastern region of Brazil and yielded solasodine in moderate to high yield.

Keywords: Solanum crinitum, S. rhytidoandrum, S. stipulaceum, S. jabrense, Solanaceae, alkaloids, solasodine.

INTRODUCTION

The genus Solanum is considered to be one of the largest among the Angiosperms and is comprised of about 1500 species (D'Arcy 1991) with at least 5000 published epithets (Nee, 1999). The genus is well represented in the northeast of Brazil with about 80 species which are widely distributed in the region. About 20 of these Solanum species are endemic to the northeastern region (Agra, 1999). Many Solanum species in the northeast are widely used in popular medicine and commonly known as "jurubeba" which is derived from the Tupi-guarani word "yu'beba", referring to the presence of prickles on some of them (Agra; Bhattacharyya, 1999). The presence of the steroidal alkaloid solasodine, which is potentially an important starting material for the synthesis of steroid hormones, is characteristic of the genus Solanum. Our continued interest (Bhattacharyya, 1984; Bhattacharyya, 1985; Barbosa Filho et al, 1991, Agra; Bhattacharyya, 1999; Silva et al., 2002) in the chemistry, pharmacology and chemotaxonomy of the genus Solanum led us to investigate four more species, three of which belonging to the subgenus Leptostemonum namely, S. crinitum Lam., S. jabrense Agra & M. Nee and S. rhytidoandrum Sendtn and S. stipulaceum Roem. & Schult. belonging to the subgenus Brevantherum, all of which are native of the northeastern region of Brazil. The fruits of all of these four species yielded solasodine which is the subject matter of the present study.

MATERIALS AND METHODS

Plant material

All the plant material were collected in northeastern Brazil and identified by M. F. Agra, the Head of the Botany Section of LTF-UFPB. The berries of S. jabrense (Agra et al. 4743, 5257)and S. stipulaceum (Agra et. al 1948, 3845)were collected from Maturéia, Serra de Teixeira, and those of S. rhytidoandrum (Agra & Bhattacharyya 1759) were collected from Areia, all in the State of Paraiba. On the other hand, the large fruits of S. crinitum (Agra et. al. 2246) were collected from Teresina, in the State of Piauí. The voucher specimens are deposited at the Herbarium Prof. Lauro Pires Xavier (JPB) and the duplicates are kept in the collection of references at LTF, both at the campus of the Universidade Federal da Paraíba, João Pessoa, Brazil.

Extraction and identification

The dried and pulverized fruits were repeatedly extracted with EtOH-H₂O-HOAc (90:8:2) until the last extracts were practically colorless. The combined extract was concentrated in vacuo, treated with 10% HOAc and then left for standing overnight. The product was filtered through a bed of Celite, the acid aqueous filtrate was basified with NH₄OH and left for standing overnight. The gelatinous precipitate was collected by filtration to give a mixture of glycoalkaloids. The alkaloid mixture was then refluxed with 15% HCl in EtOH for 3hr and subsequently left for standing overnight. The crystalline BHCl of the alkaloids were collected by filtration, suspended in 20% NH₄OH and heated for 1 hr. After cooling, the precipitated colorless solid was collected by filtration to yield a crude alkaloid fraction. The fruits of all four plants were treated in the manner described above. The crude alkaloid fraction from S. crinitum showed only one major spot on the TLC (Silica Gel plates, E. Merck, developed with 5% MeOH in CHCl₃ and visualized with Dragendorff reagent). The alkaloid fraction was crystallized from EtOH to give a colorless solid (2.0 %), m.p. 199-201º. The crude alkaloid fractions obtained from the fruits of S. stipulaceum, S. rhytidoandrum, and S. jabrense, yielded upon crystallization white solids, all with mps in the range 199-201ºC in 1.6, 1.6, and 1.0% yields, respectively.

RESULTS AND DISCUSSION

The white crystalline solids obtained from the crude alkaloids from all the four species, S. crinitum, S. rhytidoandrum, S. stipulaceum and S. jabrense, all melting in the range 199-201ºC were identified as solasodine by comparison (mmp, IR, ¹³C NMR) with an authentic sample of the alkaloid available in our laboratory. The crude alkaloid fraction of S. stipulaceum upon crystallization showed (TLC) in addition to solasodine the presence of a minor quantity of another more polar alkaloid in the mother liquor and further investigation is in progress. The crude alkaloid fractions of the remaining plants showed only one spot on TLC plates which proved to be that of solasodine.

ACKNOWLEDGEMENTS

The partial financial support of the CNPq in the form of fellowships (T.M.S. Silva and M.F.Agra) and CAPES (J.B.) are gratefully acknowledged. Thanks are also due to Dulce Goncalves de Oliveira for technical assistance and Prof. Delby Fernandes de Medeiros, the founder director of this laboratory for his constant encouragement and interest.

Received 09/21/05

Accepted 11/22/05

• Agra MF 1999. Diversity and distribution of Solanum subgenus Leptostemonum in north east Brazil. In Nee, M., Symon, D.E., Lester, R.N., Jessop, J.P. Solanaceae IV: advances in biology and utilization Royal Botanic Gardens, Kew, pp. 197-203.
• Agra MF, Bhattacharyya J 1999. Ethnomedicinal and phytochemical investigation of Solanum species in northeast Brazil. In Nee, M., Symon, D.E., Lester, R.N. & Jessop, J.P. Solanaceae IV: advances in biology and utilization Royal Botanic Gardens, Kew, pp. 341-343.
• Barbosa-Filho JM, Agra MF, Oliveira RAG, Trolin G, Cunha EVL, Bhattacharyya J 1991. Chemical and pharmacological investigation of Solanum species of Brazil: a search for solasodine and other therapeutic agents. Mem I Oswaldo Cruz 86: 181-184.
• Bhattacharyya J 1984. Isolation of solasodine from the fruits of Solanum asperum and Solanum paludosum J Nat Prod 47: 105-109.
• Bhattacharyya J 1985. Stucture of solaparnaine, a new spirosoalane alkaloid from the green berries of Solanum asperum Heterocycles 23: 3111-3113.
• D'arcy WG 1991. The Solanaceae since 1976 with a review of its biogeography. In Hawkes, J. G., Lester, R. N., Nee, M., Estrada-R., N. (editors) Solanaceae III: Taxonomy, chemistry, evolution. Royal Botanic Gardens, Kew. pp. 75-137.
• Nee M 1999. Synopsis of Solanum in the new world. In Nee, M., Symon, D.E., Lester, R.N. & Jessop, J.P. Solanaceae IV: advances in biology and utilization Royal Botanic Gardens, Kew, pp.285-333.
• Silva TMS, Braz-Filho R, Carvalho MG, Agra MF 2002. 1,2,3,4-Tetrahydro-2-methyl-b-carboline and solavetivone from Solanum jabrense. Biochem Syst Ecol 30: 1083-1085.

Publication Dates

• Publication in this collection
  05 May 2008
• Date of issue
  Dec 2005

History

• Accepted
  22 Nov 2005
• Received
  21 Sept 2005