No abstract

Apelin is an important contributor to the renin-angiotensin axis, regulating cardiovascular, metabolic, and neurological functions. Apelin-17 has especially potent cardio-physiological effects but is rapidly degraded in human blood (t 0.5 ∼ 4 min). Angiotensin-converting enzyme 2 (ACE-2), neprilysin (NEP), and plasma kallikrein (KLKB1) cleave and inactivate it, with the latter cutting within the arginine−arginine site. Here, we show that analogues with an N-terminal polyethylene glycol (PEG) extension as well as peptide bond isosteres resist KLKB1 cleavage but that only the PEG-extended analogues significantly improve physiologically activity. The PEGylated analogues feature comparatively high log D 7.4 values and high plasma protein binding, adding to their stability. An alanine scan of apelin-17 reveals that the integrity and conformational flexibility of the KFRR motif are necessary for cardio-physiological activity. An optimized Cbz-PEG 6 analogue is presented that is stable in blood (t 0.5 ∼ 18 h), has significant blood-pressure lowering effect, and shows fast recovery of heart function in Langendorff assay.

The hallucinogenic plant, Salvia divinorum, synthesizes neoclerodane diterpenes, such as salvinorins, salvidivins, and salvinicins, which are agonistic or antagonistic to μor κ-opioid receptors. From S. divinorum trichomes, crotonolide G synthase (SdCS; CYP76AH39) was identified. It catalyzes the conversion of kolavenol to a dihydrofuran neoclerodane, crotonolide G. 18 O 2feeding studies confirmed that SdCS incorporates an aerobic oxygen into crotonolide G, rather than forming a cation at C16 that is trapped by the alcohol at C15. Structural modeling of SdCS accompanied by site-directed mutagenesis established the importance of V367 and F479 residues in substrate-binding. The dihydrofuran neoclerodane can serve as a unique lead structure for drug development.

Syntheses of stereochemically pure and selectively protected diamino diacids can be achieved by redox decarboxylation of distal N-hydroxyphthalimide esters of protected aspartic, glutamic or α-aminoadipic acids via radical addition to methylideneoxazolidinones. The products are useful for solidsupported syntheses of robust bioactive carbocyclic peptide analogs. Yields of reactive primary radical addition are superior to those of more stabilized radicals, and the reaction fails if the alkylideneoxazolidinone has a methyl substituent on its terminus (i.e., 13a/13b).

Neopetrosiamide, a 28-residue peptide from Neopetrosia sp., contains three disulfide bonds and hinders mammalian tumor cell invasion. Proper connectivity of disulfide bonds is crucial for activity. Synthetic replacement of single disulfide bridges with methylene bridges gives active analogues. Pre-stapling of one ring enhances the correct formation of the remaining disulfides by reducing isomeric possibilities and possibly initiating the correct 3D fold. Cloning and expression of neopetrosiamide in E. coli affords access to the natural linear peptide.Letter pubs.acs.org/OrgLett