Actinomycetes have always attracted attention as potential candidates warranting extensive investigation, because of their ability to produce pharmaceutically useful compounds. However, in recent years, the rate of the discovery of novel compounds from these bacteria has decreased significantly.1,2 As a consequence, it is now more important than ever to isolate actinomycetes from a wide variety of environmental sources and employ various isolation methods to obtain new bioactive compounds. In our efforts to isolate novel secondary metabolites, we have focused on mangrove soil as a rich source of diverse actinomycetes.On the other hand, malignant pleural mesothelioma (MPM), which is associated with exposure to asbestos fibers, is an aggressive neoplasm developing from the pleura and is highly invasive to surrounding tissues.3–5 MPM has been demonstrated to be resistant to all conventional therapies, including chemotherapy, radiotherapy and surgery, and the prognosis of patients remains very poor. Consequently, it is a tumor that continues to be a difficult clinical problem.3–5 Therefore, development of novel therapeutic agents against MPM is strongly desired. In the course of our screening program for cytotoxic compounds against MPM cells, we have already discovered several novel anti-MPM compounds, namely, JBIR-23,6,7 the teleocidin analog JBIR-31,8 the aminocaprophenonealkaloid ficuseptamine B,9 the 1,1-dichlorocyclopropane-skeletoncontaining angucycline JBIR-88,10 the angucycline analogs JBIR-90- 93 and -116,11 the xanthoquinodin analogs JBIR-97-99,12 and the macrocyclic dilactone JBIR-101.13 As a result of further screening using MPM cells, we have discovered a new cyclizidine analog, termed JBIR-102 (1), from a culture of Saccharopolyspora sp. RL78,14 found in a mangrove soil sample (Figure 1a). This manuscript describes the fermentation, isolation, structural elucidation and, briefly, the biological activity of 1.