A reinvestigation of the anthrone derivative 4-hydroxyaloin as main product of the mild IN VITRO-oxidation of aloin has led to the revision of the proposed structure as the aloin-analogous oxanthrone derivative, the new 10-hydroxyaloin, which was prepared from aloin by an improved procedure in ammonia at pH 9. 10-Hydroxyaloin was separated into its C10-diastereomers A and B by analytical and preparative chromatographic methods. Their structures were elucidated by spectroscopic methods (FAB-MS; (1)H/ (13)C-NMR; CD), which show that 10-hydroxyaloin A is the 10 R,1' R compound and that 10-hydroxyaloin B has the 10 S,1' R-configuration.

Almost 140 years after the first isolation of the principal component aloin of the world‐wide used drug Aloe barbadensis, the absolute configuration of aloin B 1 at C10 has now been established by an X‐ray structure analysis as R and thus that of aloin A as S. The instability of the two diastereomers in solution had hitherto prevented the cultivation of single crystals.

Almost 140 years after the first isolation of the principal component aloin of the world‐wide used drug Aloe barbadensis and Aloe capensis, the absolute configuration of aloin B (I) and aloin A (II) at C‐10 can now be established by an X‐ray analysis of (I).

Umsetzung von 5 mit dem Vilsmeier-Reagenzrsl (Chlordimethylformamidiniumchlorid) wurde Verbindung 6 erhalten, die sich rnit 7 in situ unter Helferi~h-Bedingungen[~] in Ether zu 8 kuppeln liefl [Ausbeute: 76%; [a];' + 32.4 (c = 1.05, CHCI,); 300 MHz-'H-NMR (CDCI,, TMS): 6 =

Rhamnus purshianus D. C., 10-Hydroxyaloins A/B, Oxanthrone Glucosyls, Quinonoids, AnthranoidsThe absolute configurations of the diastereomeric 10-hydroxyaloins, which may be regarded as parent structures for other naturally occurring oxanthrone-C-glucosyls, have been established as 10R, 16 R (A) and 10 S, 16 R (B) by an X-ray structure analysis of the A-octaacetyl derivative (C 16 is the anomeric glucosyl carbon atom). The determination was confirmed by CD spectroscopic comparison with the structural analogues aloins A and B, which should prove useful for making future configurational assignments within this class of compounds. A conformational analysis by the use of a molecular modeling method based on force-field calculations reveals the presence of an extra- and an intra-form, the extra-form of which is energetically preferred.