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Three tricyclic dilactams were investigated as models for study of chiroptical properties of homoconjugated non-planar cis-amide groups. Racemic 5,8-diazatricyclo[6,3,0,01,5]undecane-4,9-dione (I) was partially resolved into enantiomers by chromatography on acetylcellulose. The 6-isobutyl (II) and 6-methyl (III) derivatives were prepared in optically pure forms by condensation of diethyl 4-oxoheptanedioate with (S)-1,2-diamino-4-methylpentane and (S)-1,2-diamino-propane, respectively. The respective diamines were synthesized starting from (S)-leucine and (S)-alanine: this determined the absolute configuration on the C(6) atom in both dilactams. As shown by 1H and 13C NMR spectra, the condensation reaction afforded only one of the two possible diastereoisomeric dilactams. The configurational relation between the chiral center at C(6) and the chirality of the tricyclic moiety was derived from coupling constants in the 1H NMR spectra. The configuration of compound II was confirmed by X-ray diffraction. According to 1H NMR spectra, the spatial arrangement of II in solution is similar to that in crystal, the only difference being in the local conformation of the isobutyl side chain at C(6). IR spectroscopy identified only minor differences in geometry of the two lactam groupings in II and III. All CD parameters of compounds I-III, measured in various solvents, are very similar. The CD curves show the same absolute configuration (1S, 6S) of compounds II and III and the opposite configuration of the studied enantiomer of I(1R). Parameters of the n-π dichroic band indicate a non-planar amide-grouping whose geometry is known from the X-ray analysis. Its sign agrees with the relationship derived for the chiroptical properties of defined pyramidicity on nitrogen atom in non-planar amides. The π-π dichroic bands exhibit an exciton splitting into a couplet as a result of interaction between the amide groups.

Dedicated to Professor Holger Erdtman on the occasion 0/ his 80th birthday.From the endemic Cuban species Rauuol/ia salicl/olia GRISEB nine alkaloids were isolated of which the following seven had been already described: ( + )-ajmalidine (I), ( -)-reserpiline (11), ( -)-iso-The structure of ( -)-raucubaine (VI11) had been previously determined by X-ray diffraction and the structure of the alkaloid (-)-raucubainine (IX) was suggested on the basis of its conversion to ( -)-raucubaine (V Ill). The absol ute configuration of ( -)-raucubaine and (-)-raucubainine was elucidated by CD spectroscopy.Rau volfia salicifolia GRISEB represents one of the three endemic Cuban species of the Rauvolfia genus. This species was phytochemically studied in 1957 by Korzun and coworkers! who proved the presence of deserpidine, reserpiline, rescinamine and reserpine in the extract. The alkaloids were characterized only by paper chromatographic comparison with the authentic compounds.In this study we describe the isolation of nine alkaloids: From the root bark we isolated (+ )-ajmalidine (I), (-)-reserpiline (II), (-)-isoreserpiline (III) and ( -)-isocarapanaubine (IV). The principal alkaloid present in the plant is reserpiline. Isocarapanaubine was isolated from the Rauvolfia genus for the second time, the first isolation being from Rauvolfia vo mitoria 2 • From the tree bark we obtained ( -)-reserpiline (II), ( -)-ajmalicine (V), ( + )-vellosimine (VI) and ( + )-yohimbine (VII). The leaves afforded ( -)-reserpiline (II), ( -)-ajmalicine (V) and the new alkaloids (-)-raucubaine (VIII) and (-)-raucubainine (IX).The structure of raucubaine (VIII) was determined already by X-ray analysis 3 ,4.Its IH-NMR spectrum displays signals of four arom atic protons whose mutual interactions indicate an ortho-disubstituted benzene nucleu s, a singlet at (5 2·71 due Part XLVI in the series Plant Substances; Part XLV: This Journal 47, 644 (1982). This work represents part of the Thesis of P. Sierra

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