ALKALOIDS OF THE AFRICAN RAUWOLFIA SPECIES OF THE SUB-SECTION OPHIOXYLANTHUS

ALKALOIDS OF THE AFRICAN RAUWOLFIA SPECIES OF THE SUB-SECTION OPHIOXYLANTHUS

Abstract:

The a l k a l o i d s of t h e Rauwolfia s p e c i e s have been reviewed and s p e c t r o s c o p i c methods of i d e n t i f i c a t i o n d i s c u s s e d. D e t a i l e d phytochemical i n v e s t i g a t i o n s have “been c a r r i e d out on t h e two s p e c i e s of t h e s e c t i o n Ophioxylanthus of P i c h o n ‘ s c l a s s i f i c a t i on of t h e genus Rauwolfia. In a l l , n i n e t y a l k a l o i d s were i s o l a t e d and t h e i r s t r u c t u r e s e l u c i d a t e d. R. v o l k e n s i i s t a p f root y i e l d e d t w e n t y – s i x a l k a l o i d s i n c l u d i ng two new compounds, t e t r a p h y l l i c i n e – 1 7 – O – a c e t y l and r a u v o l c i n i n e . The stem b a r k gave s e v e n t e e n a l k a l o i d s i n c l u d i n g t h e new a l k a l o id p r e – p e r a k i n e . Thirteen a l k a l o i d s were i s o l a t e d from t h e l e a v e s , four of which are new n a t u r a l p r o d u c t s i . e . m e t h o x y – p l e i o e a r p a m i n e , methoxyp l e i o c a r p a m i n e 2 : 7 d i h y d r o , methoxy-pleioearpamine N-oxide and v o l k e n s i n e . The a l k a l o i d p l e i o c a r p a m i n e and i t s d e r i v a t i v e s have not p r e v i o u s l y been i s o l a t e d from any Rauwolfia s p e c i e s. l\- o r e o g i t o n Mgf. root y i e l d e d t h i r t e e n a l k a l o i d s of which t h r ee have not been p r e v i o u s l y r e p o r t e d i n t h e p l a n t . The l e a v e s y i e l d ed t w e n t y – o n e a l k a l o i d s i n c l u d i n g f i v e new ones , akuammiline-5-formyl, o r e o g U, akuammiline 2 – d i h y d r o , d e a c e t y l akuammiline 2/4 – d i h y d r o and an i m p o r t a n t b i o g e n e t i c i n t e r m e d i a t e a l k a l o i d a d i r u b i n e a c e t a t e 19 : 20 dehydro. The i n t e r – r e l a t i o n s h i p of t h e i s o l a t e d a l k a l o i d s has been d i s c u s s ed and b i o s y n t h e t i c pathways proposed. The evidence o b t a i n e d concerning the a l k a l o i d s of t h e s e c t i o n Ophioxylanthus s p e c i e s has been used t o r e l a te t h e s e c t i o n chemotaxonomically to t h e o t h e r African Rauwolfia s e c t i o n s and t h e c l o s e l y r e l a t e d genus Cabucala.

ALKALOIDS OF THE AFRICAN RAUWOLFIA SPECIES OF THE SUB-SECTION OPHIOXYLANTHUS