In a preliminary note [1] we established the plane structure of the prosopine 1,2‐hydroxymethyl 3‐hydroxy 6‐dodecyl 11°‐hydroxypiperidine and the prosopinine 8, 2‐hydroxymethyl 3‐hydroxy 6‐dodecyl 10°‐keto piperidine, alkaloids isolated from Prosopis africana (Guill & Perr) Taub. This paper contains the study of the reduction products of the pyrrolidine 18b and the establishment of the relative and absolute configurations of these two alkaloids. The experimental part involves the details for the determination of these structures and also the extraction method of these two alkaloids as well as the new alkaloids: prosophylline, prosafrine and the prosafrinine isolated from leaves of P. africana and isoprosopinines A and B extracted from roots and stem bark of the same plant. The establishment of the structure of the new five alkaloids is the subject of the next paper.

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The structures of five new alkaloids have been established: the isoprosopinines A and B, 1 and 2 are homogeneous mixture: isoprosopinine A is (2R, 3S, 6R) 2‐hydroxymethyl 3‐hydroxy 6‐dodecyl 7°‐keto piperidine and isoprosopinine B is (2R, 3S, 6R) 2‐hydroxymethyl 3‐hydroxy 6‐dodecyl 8°‐keto piperidine. Prosophylline 4 is d 2‐hydroxymethyl 3‐hydroxyl 6‐dodecyl 10°‐keto piperidine, prosafrine 9 is (2R, 3R, 6S) 2‐methyl 3‐hydroxy 6‐dodecyl 10°‐hydroxy piperidine and prosafrinine 11, is (2R, 3R, 6S) 2‐methyl 3‐hydroxy 6‐dodecyl 10°‐keto piperidine.

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