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The pathogenesis of type II diabetes is associated with the aggregation of the 37-residue human islet amyloid polypeptide (hIAPP) into cytotoxic beta sheet aggregates and fibrils. We have recently shown that introduction of two N-methyl rests in the beta sheet- and amyloid-core-containing sequence hIAPP(22-27), or NFGAIL converted this amyloidogenic and cytotoxic sequence into nonamyloidogenic and noncytotoxic NF(N-Me)GA(N-Me)IL. Here, we show that NF(N-Me)GA(N-Me)IL is able to bind with high-affinity full-length hIAPP and to inhibit its fibrillogenesis. NF(N-Me)GA(N-Me)IL also inhibits hIAPP-mediated apoptotic beta cell death. By contrast, unmodified NFGAIL does not inhibit hIAPP amyloidogenesis and cytotoxicity, suggesting that N-methylation conferred on NFGAIL the properties of NF(N-Me)GA(N-Me)IL. These results support the concept that rational N-methylation of hIAPP amyloid-core sequences may be a valuable strategy to design pancreatic-amyloid diagnostics and therapeutics for type II diabetes.

Our studies suggest that ProIAPP has typical properties of an amyloidogenic polypeptide but also indicate that the pro-region suppresses the amyloidogenic and cytotoxic potentials of IAPP.

The aggregation process of beta-amyloid peptide Abeta into amyloid is strongly associated with the pathology of Alzheimer's disease (AD). Aggregation may involve a transition of an alpha helix in Abeta(1-28) into beta sheets and interactions between residues 18-20 of the "Abeta amyloid core." We applied an i, i+4 cyclic conformational constraint to the Abeta amyloid core and devised side chain-to-side chain lactam-bridged cyclo(17, 21)-[Lys(17), Asp(21)]Abeta(1-28). In contrast to Abeta(1-28) and [Lys(17), Asp(21)]Abeta(1-28), cyclo(17, 21)-[Lys(17), Asp(21)]Abeta(1-28) was not able to form beta sheets and cytotoxic amyloid aggregates. Cyclo(17, 21)-[Lys(17), Asp(21)]Abeta(1-28) was able to interact with Abeta(1-28) and to inhibit amyloid formation and cytotoxicity. Cyclo(17, 21)-[Lys(17), Asp(21)]Abeta(1-28) also interacted with Abeta(1-40) and interfered with its amyloidogenesis. Cyclo(17, 21)-[Lys(17), Asp(21)]Abeta(1-28) or similarly constrained Abeta sequences may find therapeutic and diagnostic applications in AD.

The first total synthesis of the cyclodepsipeptide chondramide A (2 b) is described. This depsipeptide is composed of four subunits, namely L‐alanine, N‐Me‐D‐tryptophan, 3‐amino‐2‐methoxy‐propionic acid (β‐tyrosine derivative), and a 7‐hydroxy‐alkenoic acid. While the configuration of the stereogenic centers in the 7‐hydroxy‐alkenoic acid were known, the configuration of the tyrosine derivative required clarification and turned out to be (2S,3R) or (2L,3L), respectively. The synthesis of the 3‐amino‐2‐methoxy‐3‐arylpropanoic ester 20 b relied on an asymmetric dihydroxylation yielding diol ent‐15 a followed by a regioselective Mitsunobu substitution leading to 3‐azido‐2‐hydroxypropanoate 18 b. We could also show that the ester bond in the seco compound 26 b can be fashioned by a Mitsunobu esterification by using hydroxy ester (7S)‐7 and the tripeptide acid 25 b. This synthesis should allow for the preparation of various analogues.

Starting from cinnamates 9, obtained by Wittig reaction or Heck coupling, the diols 17 were prepared by asymmetric dihydroxylation. This was followed by a regioselective substitution of the 3-OH group with hydrazoic acid under Mitsunobu conditions. Methylation of the 2-OH group and reduction of the azide group led to the β-tyrosine derivatives 8. Condensation with the dipeptide acid 6 furnished the tripeptide part of the chondramides. The derived acids 21 were combined with the hydroxy ester 7 to the esters 22. Cleavage of the tert-butyl groups and intramolecular lactam formation gave rise to the chondramide A analogues 2b–k. Growth inhibition assays showed most of the analogues to be biologically active. Some of them even reach the activity of jasplakinolide. It can be concluded that the 4-position of the aryl ring in the β-tyrosine of chondramide A tolerates structural modifications quite well.

The use of Kobayashi vinylogous aldol reaction in the reaction with acetaldehyde led to anti-aldol product 11. After reductive removal of the chiral auxiliary, the primary alcohol was converted to the allyliodide 14. This compound could be engaged in an Evans alkylation reaction, leading eventually to hydroxy acid 19. Inclusion of a Mitsunobu inversion reaction on the sequence starting with ent-11 led to hydroxy ester 30, featuring a 6,7-syn-configuration. These hydroxy acids should help to elucidate the correct stereostructure of the chondramide depsipeptides.

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