Novel propanamide analogue and antiproliferative diketopiperazines from mangrove Streptomyces sp. Q24

A new propanamide analogue (1), along with one known alkaloid (2) and four known diketopiperazines (3-6), was isolated from a cultured broth of the actinomycete Streptomyces sp. Q24 that was obtained from a sample of mangrove soil. The structures of these isolates were characterised as 3-acetylamino-N-2-thienyl-propanamide (1), N-acetyltryptamine (2), cyclo-(l-phenylalanine-l-4-hydroxyproline) (3), cyclo-(l-leucine-l-4-hydroxyproline) (4), cyclo-(l-phenylalanine-d-4-hydroxyproline) (5) and cyclo-(l-leucine-l-proline) (6) based on their NMR and HRESIMS data as well as optical rotation. Three diketopiperazines (3, 4, 6) showed activity in inhibiting the proliferation of human glioma U87-MG and U251 cells. This type of the new propanamide analogue (1) is first found from a nature source and the antiproliferative property of these three diketopiperazines against glioma cells is also reported herein for the first time.