Natural products are considered to be good sources for the screening of lead compounds of clinical drugs. We performed many drug screenings employing a variety of assay systems with crude extracts of microbial cultures as a traditional natural product library. In some assay systems, effective application of our crude extract library was difficult without making some improvements. From this viewpoint, we started to construct a purified natural compounds library from cultures of microorganisms. To achieve this, we established the highthroughput detection system for microbial secondary metabolites using UPLC-UV-evaporative light-scattering (ELS)-MS system, and more than 1000 compounds, which we have already isolated, were analyzed by the common analytic method and in our database. The registered compounds in microbial cultures are automatically identified with our system, which allows us easily to pick up unregistered compounds. The unregistered compounds are isolated from the cultures and store in our library. Because Aspergillus species are known to produce more than 950 documented bioactive compounds such as mevinolin, aflatoxin and citrinin,1 their secondary metabolites are an important source to obtain various bioactive compounds. Therefore, we attempted to obtain secondary metabolites from cultures of Aspergillus. During chemical screening based on our analytic system, we isolated a new janthitrem derivative named JBIR-137 (1) and a novel metabolite JBIR-138 (2), together with the known compounds, a tremorgenic agent janthitrem B2 and 6-hydroxycyclopiamine B3 from the culture of Aspergillus sp. fA75 (Figure 1). This paper describes the fermentation, isolation, structural elucidation, and briefly, biological activity of 1 and 2.