Isolation and antibacterial activity of phenylpropanoid derivatives from Ballota nigra

In addition to the previously isolated phenylpropanoid glycosides verbascoside 1, forsythoside B 2, arenarioside 3 and ballotetroside 4, another four compounds were isolated from generative aerial parts of Ballota nigra: three phenylpropanoid glycosides, alyssonoside 5, lavandulifolioside 6 and angoroside A 7 and a non-glycosidic derivative (+)-(E)-caffeoyl-l-malic acid 8.The antibacterial activity of the five major compounds (1–4 and 8) was tested against Gram-positive and Gram-negative bacteria. Three of them (1–3) exhibited a moderate antimicrobial activity against Proteus mirabilis and Staphylococcusaureus including one methicillin-resistant strain.