Previously, activation of the cryptic nam gene cluster led to three new naphthalenic ansamycins with unprecedented n-pentyl and n-butyl side chains from the mutant Streptomyces sp. SR201nam1OE strain. In this study, we further characterized the products of the mutant strain and six new neoansamycin congeners, namely neoansamycins D–I (1–6), were elucidated. Among them, compounds 1–3 feature the conserved skeleton of neoansamycins B and C but with n-hexyl side chains, and 4–6 are modified neoansamycins with n-pentyl side chains, illustrating the biosynthetic plasticity and diverse post-PKS modifications of neoansamycins.