Four pairs of proline-containing cyclic dipeptides from sp. HT88, an endophytic bacterium of L.

Strain HT88 was isolated from the fresh stems of , and it was identified as sp. by analyzing its morphology and the 16S rRNA sequence. The extracts of fermented HT88 showed potent antimicrobial activities. Bioassay guided separation of extracts led to eight proline -containing cyclic dipeptides. Their structures were determined by 1D and 2D NMR spectroscopy and ESI mass spectrometry and further comparison with existing H and C NMR, melting points and specific rotation data. The eight 2,5-diketopiperazines (DKPs) were identified as cyclo(-Pro-Leu) (), cyclo(Pro-Leu) (), cyclo(--Hyp--Leu) (), cyclo(--Hyp--Leu) (), and cyclo(-Pro--Phe) (), cyclo(-Pro--Phe) (, and cyclo(--Hyp--Phe) (), cycloHyp-Phe) (), respectively. Up to date, this is the first isolation of four pairs of proline based DKPs from sp.