Cyclic peptides containing non‐proteinogenic amino acids often exhibit a broad bioactivity spectrum and many have entered clinical trials with good prospects for drug development. We recently reported the discovery of six cyclic tetrapeptides, the pseudoxylallemycins A–F (1–6), from a termite‐associated Pseudoxylaria sp. X802. These compounds contain a rare O‐homoallenyl‐L‐tyrosine moiety and showed promising antimicrobial activity against the Gram‐negative pathogenic bacterium Pseudomonas aeruginosa. To perform more detailed structure‐activity studies, we pursued a precursor‐directed diversification strategy. Here, we report the purification, identification and testing of 21 new pseudoxylallemycin derivatives.

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