Konbu'acidin A, a new bromopyrrole alkaloid with cdk4 inhibitory activity from Hymeniacidon sponge

Structural Assignment of Tetrabromostyloguanidine: Does the Relative Configuration of the Palau'amines Need Revision?

“…The published configurations for 2 a, 3 c, and 4 show the protons H11, H12, H17, and H18 of the cyclopentane ring to be aligned to one side of the molecular plane, [10][11][12] which result in short distances between these four protons. However, Kinnel et al reported a weak ROESY correlation from H11 to H17.…”

“…Tetrabromostyloguanidine (1) possesses a hexacyclic core structure with a molecular constitution identical to that of dibromostyloguanidine (3 c) [10] and related to konbuacidin A (4). [11] The similar chemical shifts in the 13 C NMR spectrum for the eight stereogenic centers of 1 compared to dibromostyloguanidine (3 c) [10] and konbuacidin A (4) [11] suggested an identical relative configuration for all three compounds ( Figure 1). Dibromopalauamine (2 c) [12] was also isolated from the same sponge specimen as tetrabromostyloguanidine (1), thus providing the opportunity to compare the relative configuration of 1 directly to a palauamine derivative.…”

The Pursuit of Palau'amine

“…The relative configuration of this center in the palauamine congeners differs within the first four reports. [7,13,14] In the original studies of palauamine (1,1993), styloguanidine (19,1995), and konbuacidin A (23, 1997) the configuration at C20 was assigned as R (reference center C6 was R configured). In the second study on palauamine (1,1998) the configuration at C20 was inverted.…”

“…In 1993, Scheuer and co-workers reported the structure of palauamine (1, Scheme 1), [7] an architecturally interesting alkaloid from the same family. Since then, the pyrroleimidazole alkaloid family (Scheme 2) has been steadily growing, with the isolation of many analogues of sceptrin (3)(4)(5)(6)(7), [8] the ageliferins (8)(9)(10), [9] the nagelamides (11-13), [10] the axinellamines (14)(15)(16)(17), [11] massadine (18), [12] the styloguanidines (19)(20)(21)(22), [13] the konbuacidins (23 and 24), [14] brominated palauamines (26 and 27), [7b] and the stunning tetrameric stylissadines (28 and 29). [15] Recently, the structure of palauamine was called into question and was revised based on a combination of advanced spectroscopic analysis, computation, and even biosynthetic considerations.…”

Strukturaufklärung des Tetrabromstyloguanidins: Muss die relative Konfiguration der Palau'amine revidiert werden?

“…Die Tatsache, dass die 13 C-Verschiebungen der acht stereogenen Zentren von 1 mit den Werten für 3 c [10] und 4 [11] praktisch überein-stimmen, deutet auf eine identische relative Konfiguration in allen drei Molekülen hin (Abbildung 1). Die Isolierung von Dibrompalauamin (2 c) [12] aus dem gleichen Organismus ermöglichte den direkten Ver- [10] Um diesen Sachverhalt zu überprüfen, wurden die ROESY-Daten quantitativ ausgewertet, wobei zur Konfigurationsbestimmung von 1 ProtonProton-Abstände aus ROESY-Spektren mit unterschiedlichen Mischzeiten (100, 150 und 200 ms) herangezogen wurden.…”