9- Hydroxy-skytanthine

The spectral data for kinabalurine D (47) showed it to be yet another 7-hydroxy-skytanthine diastereomer but proved inadequate for definitive assignment of stereochemistry. To this end kinabalurine D was converted to the quaternary ammonium iodide salt which provided suitable crystals for X-ray analysis. Kinabalurine D differs from kinabalurines A-C in having a 4-P-methyl group and a trans ring junction in which the stereochemistry of H(5)... 

The second monoterpene alkaloid kopsone gave a molecular, ion which analysed for C11H19NO. The IR (1720 cm ) and C NMR (8 218) spectral data indicated the presence of a ketone function. Other groups indicated by the NMR spectra were two CHMe groups, an N-methyl, three methylenes (one deshielded at 8 56) and four methines (one deshielded at 8 72). These, as well as a postulated common origin of 51 and 52 from the hypothetical 9-hydroxy-skytanthine precursor 53 (Scheme 1), led to the proposed structure for kopsone. The relative stereochemistry was deduced from analysis of the H NMR spectrum. 

A new monoterpene alkaloid, kinabalurine G (330) has been obtained from the leaf extract of Kopsia dasyrachis in addition to 11 known alkaloids and the novel pentacyclic indole, danuphylline vide infra) [223]. Analysis of the spectral data allowed assignment of the gross structure as well as determination of the stereochemistry at the various centers. Kinabalurine G (330) is the AZ-oxide of 9-hydroxy-S-skytanthine, which is unknown, although a 9-hydroxy-skytanthine of unknown stereochemistry has been previously reported from Tecoma stans [224]. 

The bark of Tecoma arequipensis (Bignoniaceae) yielded a major alkaloid, (-)-S-A-nor-methylskytanthine (32), [a]D -21.5°, whose structure was established through X-ray crystallographic analysis of the N-(4-bromophenylthiourea) derivative (36). Other alkaloids detected by GC-MS analysis included 5,6-dehydroskytanthine, skytanthine, actinidine, 5-hydroxy-skytanthine and tecomanine. Additional components were partially characterized (MS data only) as two hydroxytecomanines and four... 

Originally isolated as Alkaloid C by Jones and Dickinson (45), the structure was deduced to be that of a 5- or 9-hydroxy-skytanthine derivative, with the former structure preferred. To clarify this ambiguity the methiodide salt was subjected to X-ray crystallographic analysis (46,47), which showed that the isolate was 5/3-hydroxy-skytanthine (44). The same compound was also isolated from the fruits of Tecoma starts, and the proton and 13C NMR data were established (42). 

The leaves of T. starts revealed two polar skytanthine derivatives, which were partially characterized as S-skytanthine (33), 5-hydroxy-skytanthine (44) (Rf 0.14), N-nor-methylskytanthine (32), or tecostanine (45) (Rf 0.06) by TLC (89). 

The leaves of Tecoma stans (Bignoniaceae) were studied previously (1) because of their reputed antidiabetic properties, which appear to have been traced to the monoterpene alkaloid fraction. Further studies of this plant by Lins and D arc Felicio (42) have now revealed the presence of two new alkaloids, 7-hydroxy-5,6-dehydroskytanthine (58) and 4-hydroxy-tecoman-ine (59), in the fruits of T. stans. In addition, two known alkaloids, 5/3-hydroxy-skytanthine (44) and tecomanine (55) were obtained. H and 13C NMR data for these known alkaloids were reported for the first time. 

Scheme 9. Cossy and Belotti synthesis of ( )-5/3-hydroxy-skytanthine (179) (182).

A 4-nor-7,8-dehydro-10-hydroxy-skytanthine (10) has been obtained from A. radiata [22]. Compotmd 10 and actinidine-type compound 5 are the alkaloid compounds that have been isolated from this plant species for the first time, and it is a reasonable hypothesis that the monoterpenoid structures of 10 and 5 should be derived from the previously isolated iridoids in this plant, which are known to be the biogenetic precursors of this type of alkaloids [50]. A novel skytanthine-type alkaloid named delavayine A (11) that comprises a benzoate ester has been isolated from 7. delavayi [25]. Similarly, another novel skytanthine-type alkaloid, incarviUateine E (12), possessing three incarvilline moieties has been isolated and characterized from the aerial parts of 7. sinensis [26]. Incarvine E (13) and incarvine F (14) [27] isolated from 7. sinensis and isoincarvilline (15) [28] and mairines A-C (16-18) [29] from 7. mairei are other new skytanthine-type monoterpenoid alkaloids. Compounds 16 and 18 contain a rare (5-skytanthine Af-oxide in the structure [29]. 

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