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Konstitution und absolute Konfiguration der Rhoeadin‐Alkaloide (+)‐Alpinigenin und (+)‐ cis ‐Alpinigenin

1977; Wiley; Volume: 60; Issue: 7 Linguagem: Inglês

10.1002/hlca.19770600728

1522-2675

Hasso Rönsch, Armin Guggisberg, Manfred Hesse, H. Schmid,

Berberine and alkaloids research

The constitution and absolute configuration of the rhoeadine alkaloids (+)‐alpinigenine and (+)‐ cis ‐alpinigenine. The fundamental structure of the hemi‐acetal phenylbenzazepine alkaloid (+)‐alpinigenine ( 1 ), isolated from Papaver bracteatum L INDL ., was derived essentially from 1 H‐NMR.‐ and mass‐spectra of 1 and its derivatives 7, 10 and 14 (cf. Scheme 2). The positioning of the four methoxy groups in the two aromatic rings could be deduced from the 1 H‐NMR.‐spectra of the N ‐oxides 14 and 15 in which, as a result of favourable sterical and conformational behaviour, an interaction exists between the N ‐oxide oxygen atom and one of the two ortho protons in ring C. The B/D‐ trans ‐fused 1 undergoes isomerization in 1 N HCl to cis ‐alpinigenine ( 16 ). A stereochemical correlation between bases in the trans ‐and cis ‐series was enabled via an Emde degradation of the corresponding methylacetal‐methyliodides 21 resp. 19 leading to the enantiomeric isochroman derivatives 22 resp. 23 which are achiral at C (2) (Scheme 4). The configuration at C (14) in the hemi‐acetals ( eg. 1 and 16 ) and the methyl ethers ( eg. 7 and 8 ) is discussed in detail (cf. Scheme 7). (+)‐Alpinigenine ( 1 ) has the (1 S , 2 R , 14 R ) configuration and (+)‐ cis ‐alpinigenine ( 16 ), in chloroform or acetone solution, the (1 R , 2 R , 14 R ) configuration.