Fourth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-4), www.mdpi.org/ecsoc-4.htm, September 1-30, 2000

[C0017]

Tamar Evan, Amira Rudi, Micha Ilan and Yoel Kashman

School of Chemistry and department of Zoology, Tel-Aviv University, Ramat Aviv 69978, Israel
Tel.: +972-3-6408419, Fax: +972-3-6409293, E-mail: [email protected]

Received: 7 August 2000 / Uploaded: 10 August

Abstract: Aplyzanzine A (1), a novel bisdibromotyrosine derivative has been isolated from the Indo-Pacific sponge Aplysina sp. Its structure was elucidated mainly on the basis of 1D and 2D-NMR and MS spectroscopic data. A biomimetic synthesis, which might well be the biosynthesis of 1, is suggested.

In connection with our long-standing interest in the chemistry of marine sponges, we have investigated Indo-Pacific sponges that were collected near the coast of Zanzibar. From one of the sponges, an Aplysina sp. we have isolated a new dibromotyrosine derivative (1) designated aplyzanzine A.

The genus Aplysina belonging to the Verongida sponges (order Verongida, family Aplysinidae) is well known for its dibromotyrosine metabolites [1-8]. The freshly collected sponge was frozen on site and kept frozen until needed. Freeze-dried sponge tissue (70g, dry wt) was extracted with ethyl acetate to give a brown gum (0.4g) after evaporation. The latter extract was subsequently partitioned between aqueous methanol and CCl₄, CHCl₃ and n-Butanol. The CHCl₃-phase was further fractionated by chromatography on Sephadex LH-20 (eluting with CH₂Cl₂:MeOH , 1:1) to afford aplyzanzine A (1, 15 mg, 0.02% dry wt).

Aplyzanzine A (1) [9], obtained as pale orange oil, analyzed for C₂₅H₃₃Br₄N₃O₃, from the CIMS and NMR data; the CIMS [10] showing a cluster of peaks at m/z 740/742/744/746/748, in a ratio of 1:4:6:4:1, characteristic for a tetrabrominated compound. The EIMS [11] showed a similar cluster of peaks at m/z 739/741/743/745/747 while the main peak (i.e. m/z 743) had the intensity of 4% only. The IR spectrum [12] revealed bands at 1036, 1678, 3222 and 2968 cm^-1 suggesting an ethereal C−O, an amide and an aryl CH group, respectively. The presence of an amide group was confirmed by the d _C 170.8 s and d _H 8.67 br t resonances. Furthermore, the multiplicity of the NH signal suggested a CH₂NHCO group. Additional functionalities were two NMe₂ groups (d_H 2.26 s and 2.67 s, 6H each), one aromatic methoxy group (d_C 60.4 q, d_H 3.74 s, 3H), and two para substituted symmetric aromatic rings (Table 1) � accounting, together with the amide, for the nine degrees of unsaturation of 1. From the multiplicity (DEPT experiment) and d_C - values it was clear that each ring is tetrasubstituted bearing an ethereal oxygen (d_C 152.3 s and 150.9 s, for C-4 and 15, respectively). The chemical shifts of the other ring carbon-atoms and especially the three and two bond CH-correlations, seen in a HMBC experiment (Table 1 and Figure 1) determined the alkyl-dibromophenolic structure of the two rings. A 1D INAPT experiment [13] assisted with the distinction between the close aromatic C-atom shifts. All chemical shifts of the aromatic rings are in good agreement with literature values [1]. Three additional spin systems were established by a COSY experiment (Figure 2), that is, one CH₂CH, one CH₂CH₂ and one OCH₂CH₂CH₂N system (C-7, 8; C-10, 11 and C-18�20, respectively, Table 1). All the above functional groups accounted for all the molecule�s atoms and the nine degrees of unsaturation. assemblage of the various moieties of aplyzanzine A (1) was essentially achieved from the HMBC CH-correlations (Figure 1 and Table 1) and partially also confirmed by NOE measurements (Figure 2). ²J and ³J CH-correlations from 2H-7, H-8 and Me�s 22, 23 to C-1, 2 (and 6), 8 and 9; and between 2H-11, H-13 (and 17), 2H-18 and the second aromatic ring C-atoms and, similarly, between 2H-10 and 11, 2H-18, 19, 20 and Me�s 24, 25 to their adjacent C-atoms (Figure 1) established the full structure of 1. The suggested structure was further confirmed by NOE measurements (Figure 2) and several MS fragments shown in Figure 3. All fragmentations agree well with known cleavages a to heteroatoms.

The structure of aplyzanzine A (1) point clearly to a bis-dibromotyrosine derivative. Parts of 1 are well known from other Verongida sponges metabolites (e.g. moloka�inamine [2], Figure 4). Closest in structure, however, is purealidin C reported by Kobayashi [1] from Psammaplysilla purea (Figure 4). Both 1 and the latter compound have in common the dibromotyrosine - dibromotyramine skeleton, however, they are differently substituted. To the best of our knowledge, the structure of a N,N-dimethyl tyrosine is without president as a marine natural product.

Several recently reported additional dibromotyrosine derivatives are ceretinamine [4], ceratinamides A and B [5], 7-Hydroxyceratinamine [7], and other metabolites reported by Fattorusso [6].

A suggested biomimetic synthesis of 1 is shown in Scheme 1, starting from the suitable dibromotyrosine and dibromotyramine derivatives. This synthesis can also be suggested as the biosynthesis of 1 in the sponge.

Table 1. ¹H and ¹³C NMR Data for 1^a

Figure 1. HMBC correlations of 1.

Figure 2. COSY and NOE correlations of 1.

Figure 3. EIMS fragmentation of 1.

Scheme 1. Suggested biomimetic / biogenesis for 1.

Figure 4. Aplyzanzine A (1) and the closely related purealidin C and moloka�iamine [2].

[1] Kobayashi J.; Tsuda M.; Agemi K.; Shigemori H.; Ishibashi M.; Sasaki T.; Mikami Y. Tetrahedron 1991, 47, 6617-6622.

[9] Aplyzanzine A exhibits a zero a_D value, suggesting easy racemization of the chiral a position of the tyrosine, in the sponge.

[12] IR (CHCl₃) n_max 997, 1036, 1211, 1221, 1259, 1420, 1465, 1473, 1545, 1678, 2450, 2969, 3023, 3222 cm^-1.

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