The known furostanol saponins methylprotodioscin and protodioscin and two new sulfated saponins, sodium salt of 26-O-β-glucopyranosyl-22α-methoxy-(25R)-furost-5-ene-3β,26-diol- 3-O-α-rhamnopyranosyl-(1→2)-β-4-O-sulfo-glucopyranoside (methylprototribestin) and sodium salt of 26-O-β-glucopyranosyl-22α-hydroxy-(25R)-furost-5-ene-3β,26-diol-3-O-α-rhamnopyranosyl-( 1→2)-β-4-O-sulfo-glucopyranoside (prototribestin) have been isolated from the aerial parts of Tribulus terrestris L. growing in Bulgaria. The structures of the new compounds were elucidated on the basis of 1D and 2D (DQF-COSY, TOCSY, HSQC-TOCSY, HSQC, HMBC, ROESY) NMR data, ESI mass spectra and chemical transformation.

The ozonolysis of ()-longifolene (1) in different solvents (Et 2 O, CH 2 Cl 2 , CHCl 3 , acetone) at À 808 provided quantitatively longifolene epoxide (3) as a single diastereoisomer in which the O-atom is endopositioned (Scheme 2). Upon warming to room temperature, the epoxide remained stable only in acetone and was isolated as a low-melting crystalline compound. In CH 2 Cl 2 , Et 2 O, or CHCl 3 solution, epoxide 3 rapidly rearranged to the isomeric enols 4 and 5, which underwent further rearrangement to give the exo-aldehyde 6. On standing for several weeks in CH 2 Cl 2 solution, or in CHCl 3 and Et 2 O as well, at room temperature, aldehyde 6 slowly rearranged into its epimer 7. The aldehydes 6 and 7 were isolated on the preparative scale for further synthetic use. The addition of methylmagnesium iodide to 6 and 7 provided the corresponding alcohols 13/14 and 15/16, respectively, which were isolated as pure diastereoisomers (Scheme 4). The configurations of the new chiral centers in 13 ± 16 were determined by NMR methods and X-ray crystallography.

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The 103Rh,15N coupling constants and 15N chemical shifts of XRhIII(Hdmg)2L rhodoximes (Hdmg=dimethylglyoximate, L=PPh3 or pyridine, X=halide, alkyl, haloalkyl) were extracted from gradient‐selected (1H,15N)‐HSQC experiments. Coupling between rhodium and the equatorial oxime nitrogens is large (18–21 Hz) and shows little sensitivity to the nature of the cis‐oriented ligands X and L. In contrast, coupling between rhodium and the axial pyridine nitrogen is small (6–9 Hz) for X=alkyl but increases to 16–18 Hz in the halide complexes (‘trans influence’). The structural implications are discussed in conjunction with x‐ray data. © 1997 John Wiley & Sons, Ltd.