Catellatolactams A–C, Plant Growth-Promoting Ansamacrolactams from a Rare Actinomycete of the Genus Catellatospora

Catellatolactams A–C (1–3), three novel ansamacrolactams, were isolated from the culture extract of an underexplored rare actinomycete of the genus Catellatospora. Spectroscopic and spectrometric analyses by NMR and MS elucidated the structure of 1 to be a lactamized pentaketide presumably extended on a 3-amino-5-hydroxybenzoic acid starter unit. Compounds 2 and 3 further received epoxidation and intramolecular cross-linking to incorporate a 2-indolinone unit, with a 3-amino-5-hydroxybenzoic acid pendant on 3. The absolute configurations of 2 and 3 were unequivocally established to both be 2S,6R,7R by comparison of the experimental NMR chemical shifts and ECD spectra with those predicted by DFT-based quantum chemical calculation. While 1–3 showed no appreciable antimicrobial activity or cytotoxicity, root elongation of germinated lettuce seeds was promoted by 2 and 3 at 1–10 μM.