<jats:p><jats:bold>The Structure of the Alkaloid Juliprosopine from Prosopis juliflora A. Dc.</jats:bold><jats:p>A new alkaloid, juliprosopine, has been isolated from <jats:italic>Prosopis</jats:italic> <jats:italic>juliflora</jats:italic> A. Dc. <jats:italic>(Leguminosae)</jats:italic>, for which structure <jats:bold>1</jats:bold> is proposed. The piperidine moiety could be elucidated on the basis of spectroscopic data (MS., <jats:sup>1</jats:sup>H‐NMR., <jats:sup>13</jats:sup>C‐NMR.) of juliprosopine and the derivatives <jats:bold>2–4</jats:bold>. The central hexahydroindolizine part and its substitution pattern has been determined mainly on the bases of the <jats:italic>Hofmann</jats:italic>‐degradation product <jats:bold>11</jats:bold>, which yielded the hydrogenation products <jats:bold>13</jats:bold> and <jats:bold>14</jats:bold>. By ozonolysis <jats:bold>11</jats:bold> was converted to <jats:bold>16</jats:bold> and <jats:bold>18</jats:bold>. It is proposed that juliprosopine was built up in nature by two ‘monomeric’ <jats:italic>Prosopis</jats:italic> alkaloids and one dihydropyrrol unit.