Developmental patterns of phenylpropylamino alkaloids accumulation in khat (Catha edulis, Forsk.)

Khat (Catha edulis Forsk., Celastraceae) is a perennial shrub that was introduced to Israel by Yemenite immigrants. Khat young leaves are chewed as a stimulant. The main stimulating active principles in this plant are the phenylpropylamino alkaloids (-)-cathinone [(S)-alpha-aminopropiophenone], (+)-cathine [(+)-norpseudoephedrine] and (-)-norephedrine. A novel GC-MS analysis method for the quantitative determination of phenylpropylamino alkaloids and their putative precursor 1-phenyl-1,2-propanedione in khat leaves was developed. We found a marked diversity in the phenylpropylamino alkaloids content and composition in 9 different accessions originated in seedlings and in the commercial cultivar "Mahanaim". The highest 1-phenyl-1,2-propanedione and (-)-cathinone levels occur in young leaves, the part traditionally chewed for its psycho-stimulating properties. Older leaves lack (-)-cathinone but contain the less active (+)-cathine and (-)-norephedrine. Young stems and flowers also contain 1-phenyl-1,2-propanedione, (-)-cathinone, (+)-cathine and (-)-norephedrine. We report the presence of a (-)-cathinone reductase in khat leaves capable of reducing (-)-cathinone to (+)-cathine in the presence of NADPH. We propose that (-)-cathinone is a biosynthetic precursor of (+)-cathine and (-)-norephedrine in khat leaves.