Steroids 76 (2011) 588–595 Contents lists available at ScienceDirect Steroids journal homepage: www.elsevier.com/locate/steroids An approach to the synthesis and attachment of scillabiose to steroids Filip S. Ekholm a , Gyula Schneider b , János Wölfling b,∗ , Reko Leino a,∗∗ a Laboratory of Organic Chemistry, Åbo Akademi University, Biskopsgatan 8, FI-20500 Åbo, Finland b Department of Organic Chemistry, University of Szeged, H-6720-Szeged, Dóm tér 8, Hungary article info Article history: Received 16 December 2010 Received in revised form 3 February 2011 Accepted 16 February 2011 Available online 23 February 2011 Keywords: Carbohydrates NMR spectroscopy Glycosylation Scillabiose Androst-5-en-3-ol-17-one Saponins abstract Hellebrin and transvaalin are two naturally occurring saponins with biological activity. In the present paper, we describe a high yielding route to the synthesis and coupling of their shared glycone, scill- abiose, to a model steroid. A convergent coupling strategy utilizing a scillabiose-based glycosyl donor was devised for the glycosylation. This convergent approach is appealing due to its high efficiency and simple deprotection procedure and may find further use in total synthesis of naturally occurring saponins and related compounds sharing the same glycone. Due to the widespread occurrence of this glycone in nature, the complete NMR spectroscopic characterization of all compounds prepared herein is provided as reference material. In addition, glycosylations were performed with the monosaccharide constituents of scillabiose, thereby providing a limited series of glycosylated steroids for potential future evaluation of the effects of the glycone on the overall biological activity. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Hellebrin and transvaalin are bufenolides, a subclass of saponins, and are well known for their pharmacological activities. Hellebrin has been isolated from Helleborus niger and is notori- ous for its potent cytotoxic activity [1]. In addition, hellebrin has been found to display T-cell suppressive effects and has found fur- ther use as an immunoregulatory molecule [2]. Transvaalin, also called scillaren, has been isolated from Urginea sanguinea and has been extensively used as a constituent of herbal medicines to purify blood, remove abdominal pain and backache and as an abortifacient [3]. Transvaalin is also known for its poisonous effect on livestock [4]. As shown in Fig. 1, the carbohydrate parts, scillabiose (4-O-(- d-glucopyranosyl)--l-rhamnopyranoside), of these two saponins are identical. The scillabiose moiety has also been found in Scilla maritime as the glycone part of glucoscilliphaeoside [5]. In addition to the presence in these saponins, a closely related glycon contain- ing glucuronic acid instead of glucose has been found in molecules isolated from Acrosiphonia centralis, ulva lactuca and klebsiella [6]. It is well known that the biological interactions displayed by biomolecules depend on both their aglycone and glycone struc- tures, as exemplified by the complete lack of activity of the ∗ Corresponding author. Fax: +36 62 454200. ∗∗ Corresponding author. Tel.: +358 400 707195. E-mail addresses: wolfling@chem.u-szeged.hu (J. Wölfling), reko.leino@abo.fi (R. Leino). erythromycine and daunomycin antitumor agents when the car- bohydrate part is modified or removed [7]. Due to the occurrence of scillabiose and closely related compounds in several naturally occurring biomolecules and pharmaceutically active species, we became interested in the synthesis of this glycone. In the present paper, we describe a high yielding, convergent strategy for the synthesis of the scillabiose glycone and its monosaccharide con- stituents, as well as their coupling reaction to a model steroid. Being widely distributed in nature, the scillabiose moiety is relevant from both the synthetic and analytical points of view. The synthetic methodology presented herein should thus be of interest for sev- eral areas of research. Importantly, for reference purposes, we also describe here the fully characterized 1 H and 13 C NMR spectra of all of the building blocks as well as the glycosylated steroids. 2. Experimental Reaction solvents were dried and distilled prior to use when nec- essary. All reactions containing moisture- or air-sensitive reagents were carried out under argon atmosphere. The NMR spectra were recorded with a Bruker Avance spectrometer operating at 600.13 MHz ( 1 H: 600.13 MHz, 13 C: 150.90 MHz). The probe tem- perature during the experiments was kept at 25 ◦ C unless indicated otherwise. All products were fully characterized by utilization of 1 H, 1D-TOCSY and 13 C 1D-NMR techniques in combination with DQF-COSY, NOESY, HSQC and HMBC 2D-NMR techniques by using pulse sequences provided by the manufacturer. Chemical shifts are expressed on the ı scale (in ppm) using TMS (tetramethylsi- lane), residual chloroform, acetone, H 2 O or methanol as internal 0039-128X/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.steroids.2011.02.010