Caylobolide B, a macrolactone from symplostatin 1-producing marine cyanobacteria Phormidium spp. from Florida

Abstract

A Phormidium spp. collection from Key West, Florida, afforded caylobolide B (1), an analogue of the known macrolactone caylobolide A, previously isolated from a Lyngbya majuscula collection from the Bahamas. The planar structure of 1 was determined using NMR and MS experiments. The relative configuration for subunits C7-C9 and C25-C29 was assigned using Kishi's Universal NMR Database. Caylobolide B (1) displayed cytotoxic activity against HT29 colorectal adenocarcinoma and HeLa cervical carcinoma cells with IC(50) values of 4.5 and 12.2 μM, respectively.

Figure 1

Caylobolide B (1) and closely related compound caylobolide A. The absolute configuration for C25, C27 and C29 is proposed by analogy to caylobolide A. Only the relative configuration is shown for C7 and C9, which could not be related to C25–C29.

Figure 2

Key HSQC-TOCSY correlations.

Figure 3

ESI-MS/MS of caylobolide B (1).

Figure 4

Assignment of the relative configuration of caylobolide B (1) based on Kishi's Universal NMR Database (Database 2). Δδ values between the model system and 1 are shown. The relative configuration shown is based on the best fit with the model system. The 1,3-diol is assigned as syn. The Δδ values for the characteristic central carbon of the 1,3,5-triol system suggest either anti/syn or syn/anti arrangement.