Biochemical Systematics and Ecology 30 (2002) 243–247www.elsevier.com/locate/biochemsyseco

An iridoid glucoside fromGronovia scandens(Loasaceae)

Veronica Rodrı´guez, Jan Schripsema1, Søren Rosendal Jensen*

Department of Chemistry, The Technical University of Denmark, DK-2800 Lyngby, Denmark

Received 1 February 2001; accepted 14 March 2001

Abstract

A new secoiridoid glucoside has been isolated fromGronovia scandens L. (Loasaceae),namely 6-β-hydroxysweroside. The structure was mainly elucidated by spectroscopic methods.Fuertesia domingensis, another species from the subfamily Gronovioideae appeared to lackiridoid glucosides. The chemical relationships between Loasaceae and Hydrangeaceae is dis-cussed. 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Gronovia scandens; Fuertesia dominguensis; Loasaceae; Gronovioideae; Secoiridoid glyco-side; 6-β-Hydroxysweroside

1. Introduction

In continuation of earlier work on iridoid glycosides from the family Loasaceae(Jensen et al., 1981; Damtoft et al., 1993; Rodrı´guez et al., 1997), we can nowreport the results from the two generaGronovia and Fuertesia of the subfamilyGronovioideae which has only been investigated chemically in a superficial manner.The genusGronovia with two species,G. scandens L. and G. longiflora Rose, isendemic to America.G. scandens is a herb with winding stems, adorned with stiffstinging hairs and is known in some parts of Mexico (Tamaulipas and Southeast ofMexico) as a medicinal plant (Caldero´n, 1992). It is distributed from Mexico in

* Corresponding author. Tel.:+45-4525-2103; fax:+45-4593-3968.E-mail address: srj@kemi.dtu.dk (S. Rosendal Jensen).

1 Now at: Setor de Quimica de Produtos Naturais, LCQUI/CCT, Universidade Estadual do Norte Flum-inense, Av. Alberto Lamego, 2000, 28015-620 Campos dos Goytacazes, RJ, Brazil.

0305-1978/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0305 -1978(01 )00085-0

244 V. Rodrıguez et al. / Biochemical Systematics and Ecology 30 (2002) 243–247

northern Sonora and Chihuahua to northern Peru (Shreve and Wiggins, 1964). In arecent systematic work, it was screened for iridoids and reported to contain unspeci-fied “aglucons” (Weigend et al., 2000).

The monotypic Fuertesia domingensis Urban is a liana which also has stinginghairs and is endemic to Santa Domingo. To our knowledge, no previous phytochem-ical study of this genus has been reported.

2. Materials and methods

Mps. are uncorr. In the NMR spectra the solvent peaks were used as internalstandard, except for the 13C NMR spectrum recorded in D2O, when the C6� peak wasset to d 61.5 (Damtoft et al., 1981). Gronovia scandens was grown in a greenhouse inThe Botanical Garden of The University of Copenhagen, it was kept frozen in apolyethylene bag at �23°C; the voucher (5118c-1) is kept in the Garden’s Her-barium. Fuertesia domingensis was collected in Artibonite, Santo Domingo; thevoucher (Zanoni, Mejıa, Pimentel 24495) is deposited in the Herbarium of the Mis-souri Botanical Garden.

2.1. Gronovia scandens

Frozen whole plants (700 g) were homogenized with EtOH (2×1700 ml) filtered,taken to dryness and partitioned in H2O–Et2O. The aq. layer was concd and redis-solved in MeOH to give an inorganic precipitate (3.7 g). The methanol extract waspassed through act. C on celite. Evaporation of the filtrate gave a white foam (10.3g), of which an aliquot (6.3 g) was subjected to reverse phase MPLC on a home-made column packed with Polygoprep. C18 (50–60 �m; 1.5 kg), eluting with H2O–MeOH mixtures (10:1 to 1:1). After elution of sugars and inorganics was obtainedalmost pure 6-β-hydroxysweroside

(1, 347 mg, 0.05%). The product was crystallized from EtOH, mp 177–178°C;[a]21

D = �207° (MeOH; c 0.5); lmax (MeOH): 244 nm; 1H NMR (500 MHz, D2O):d 5.70 (d, J=1.5 Hz, H1), 7.73 (d, J=2.0 Hz, H3), 3.05 (m, H-5), 4.20 (ddd, J=10.3,10.3 and 4.6 Hz, H6), 4.35 (dd, J=10.3 and 10.3 Hz, H7β), 4.60 (dd, J=10.3 and4.6 Hz, H7α), 5.65 (ddd, J=17.3, 10.2 and 8.8 Hz, H8), 3.06 (m, H9), 5.55 (dd,J=17.3 and 2.0 Hz, H10a), 5.44 (dd, J=10.2 and 2.0 Hz, H10b), 4.92 (d, J=8.0 Hz,

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H1�), 3.37 (dd, J=9.3 and 8.0 Hz, H2�), 3.57 (t-like, J=9.3 Hz, H3�), 3.48 (t-like,J=�9.5 Hz, H4�), 3.58 (m, H5�), 3.80 (dd, J=12.4 and 6.0 Hz, H6a�), 4.00 (dd, J=12.4and 2.2 Hz, H6b�); 13C NMR (63 MHz, D2O): d 98.4 (C1), 155.8 (C3), 102.3 (C4),34.5 (C5), 71.4 (C6), 63.1 (C7), 131.1 (C8), 39.8 (C9), 122.3 (C10), 169.4 (C11),99.1 (C1�), 73.4 (C2�), 76.3 (C3�), 70.4 (C4�), 77.1 (C5�), 61.5 (C6�). (Found; C,50.2; H, 6.5%. C16H22O10·1/2H2O requires: C 50.1; H 6.1%).

Pentaacetyl 6-b-hydroxysweroside (1a) was prepared by acetylation of 1 (53 mg)with pyridine and Ac2O (2:1) at r.t. for 20 h. After removal of the solvent the residuewas crystallized from MeOH (79 mg); mp. 166–167°C; 1H NMR (250 MHz, CDCl3):d 5.32 (d, J=1.5 Hz, H1), 7.51 (d, J=2.5 Hz, H3), 2.98 (ddd, J=10, 5.5 and 2.5 Hz,H5), 4.84 (ddd, J=10, 9.5 and 4.5 Hz, H6), 4.00 (dd, J=9.5 and 10.5 Hz, H7β), 4.33(dd, J=10.5 and 4.5 Hz, H7α), 5.45 (br. ddd, J=17, 10.5 and 9.5 Hz, H8), 2.83 (ddd,J=9.5, 5.5 and 1.5 Hz, H-9), ca 5.25 (unres., 10-CH2), 4.88 (d, J=8 Hz, H1�), 4.97(dd, J=9.5 and 8 Hz, H2�), 5.20 (t-like, J=9.5 Hz, H3�), 5.05 (t-like, J=9.5 Hz, H4�),3.73 (ddd, J=9.5, 4.5 and 2 Hz, H-5�), 4.26 (dd, J=12.5 and 4.5 Hz, H6a�), 4.10 (dd,J=12.5 and 2.0 Hz, H6b�); 13C NMR (63 MHz, CDCl3): δ 96.3 (C1), 152.9 (C3),101.8 (C4), 32.4 (C5), 65.1 (C-6),* 67.3 (C-7),* 129.8 (C8), 39.0 (C9), 122.0 (C10),166.5 (C11), 96.1 (C1�), 70.3 (C2�), 72.0 (C3�), 67.9 (C4�), 72.2 (C5�), 61.5 (C-6�);* interchangeable. (Found: C, 53.6; H, 5.6%. C26H32O15, requires: C 53.4; H 5.5%.)

2.2. Fuertesia domingensis

Dry leaves and stems (each 50 g) were blended with EtOH (150 ml) and left tostand for 2 d. Filtering and evaporation followed by treatment as above gave theMeOH-solubles (190 and 360 mg, respectively). In neither of these fractions iridoidscould be detected by NMR and HPLC.

3. Results and discussion

The water soluble part of an ethanolic extract of G. scandens was fractionated byreverse phase chromatography to give only a single compound (1) which could becrystallized (mp 177–178°C), and it analyzed for C16H22O10. By acetylation wasobtained a pentaacetate (1a; mp 166–167°C). The 13C NMR spectrum of 1 contained17 signals and was somewhat similar to that reported for sweroside (2; Keawpraduret al., 1994). Six signals could be assigned to a β-glucopyranosyl moiety. Theremaining 11 signals fitted reasonably with a sweroside-like structure having anadditional secondary OH-substituted carbon atom (d 75.49) like that shown in theformula 1. The 1H NMR spectrum of 1 was also similar to that of 2 (Keawpraduret al., 1994), except that the high field signals from the 6-protons in 2 at d 1.6–1.7were lacking in 1, which instead displayed a one-proton signal δ 4.20. The couplingpattern allowed assignment of all the signals, proving the position of the secondaryhydroxyl group to be at C6. The over-all stereochemistry was shown to be the sameas that of 2 since the coupling constants were essentially the same in the two com-pounds. Also the stereochemistry at C6 could be determined by the coupling pattern

246 V. Rodrıguez et al. / Biochemical Systematics and Ecology 30 (2002) 243–247

since the lactone ring in 1 apparently occupies a 5CO chair-like conformation as isalso seen in 2 (Purdy et al., 1981) and in the similar glucoside xylostosidine (Tietzeet al., 1989). Thus, H6 must be axial due to the large trans-diaxial coupling constantsJ5,6 and J6,7b, leaving the 6-OH substituent in the equatorial β-position. The newcompound is therefore 6-β-hydroxysweroside.

In a similar extract of dry material of Fuertesia domingensis no iridoids couldbe detected.

Loganin and secoiridoids appear to be characteristic for by far the most speciesof the Loasaceae (Muller et al., 1999; Weigend et al., 2000), although a few excep-tions are seen. Thus, Schismocarpus matudai solely contains a carbocyclic iridoidglucoside derived from loganin (Damtoft et al., 1993); furthermore, most of the irido-ids known from the genus Mentzelia are of a rare type lacking C-10 (Jensen et al.,1981) although a few species in addition contain secoiridoids. The present result fitswell in with the above picture.

The systematic position of Loasaceae has been much discussed, but a closerelationship between the families Loasaceae and Hydrangeaceae was first suggestedby Hufford (1992) and is also demonstrated by more recent chloroplast DNA sequen-cing results (Hempel et al., 1995; Soltis et al., 1995; Xiang et al., 1998) and by thecommon presence of loganin and secoiridoids as well as of the rare iridoids lackingC-10, the latter in only one genus in each of the two families (cf. Frederiksen et al.,1999). We can now add further chemical evidence to support this probable closerelationship. The glucoside sweroside (2) is very common in secoiridoid containingfamilies and many esters of 2 and its 5-hydroxylated derivative, swertiamarin areknown, particularly from Gentianaceae (Rodriguez et al., 1998; Jensen and Schrip-sema, 2001). Despite this, no 6-hydroxylated derivatives of 2 have been previouslypublished, however, very recently we have also found 1 and 2 together with loganinin Kirengeshoma palmata Yatabe (Hydrangeaceae) (Jensen, unpublished), indicatinganother rare biosynthetic ability to be shared by the two taxa.

Acknowledgements

Dr. Thomas A. Zanoni, now at New York Botanical Garden, and the staff at TheBotanical Garden of The University of Copenhagen are thanked for the authenticatedplant material. We also thank the Consejo Nacional de Ciencia y Tecnologıa(CONACyT), Mexico for a scholarship (No. 93059) for VR, and the EU Commissionfor a Grant to JS (BIO2-CT94-8054).

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