The relative configuration of tulearin A I (R3 = H, R8 = CONH2, R9 = H) was detd. by X-ray diffraction anal. of a cyclic carbonate deriv. I (R3 = H, R8R9 = CO), and the abs. configuration (2R,3R,5S,8S,9S,15R,17S) from the 9-MTPA-esters I [R3 = H, R8 = CONH2, R9 = COC(OMe)(CF3)Ph-(R), -(S)] was detd. using the modified Mosher's method. A mechanism for the unexpected formation of the cyclic carbonate was suggested. Two N-phenyltriazolinedione cycloadducts of tulearin A were also prepd. Two addnl. tulearins, B and C I (R3 = CONH2, R8 = CONH2, R9 = H; R3 = H, R8 = H, R9 = H, resp.), were isolated in very small amts. from Fascaplysinopsis, and their structures are elucidated by spectroscopic means. [on SciFinder(R)]