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.