From receptors in the nose to supramolecular biopolymers, nature shows a remarkable degree of specificity in the recognition of chiral molecules, resulting in the mirror image arrangements of the two forms eliciting quite different biological responses. It is thus critically important that during a chemical synthesis of chiral molecules only one of the two three-dimensional arrangements is created. Although certain classes of chiral molecules (for example secondary alcohols) are now easy to make selectively in the single mirror image form, one class-those containing quaternary stereogenic centres (a carbon atom with four different non-hydrogen substituents)-remains a great challenge. Here we present a general solution to this problem which takes easily obtainable secondary alcohols in their single mirror image form and in a two-step sequence converts them into tertiary alcohols (quaternary stereogenic centres). The overall process involves removing the hydrogen atom (attached to carbon) of the secondary alcohol and effectively replacing it with an alkyl, alkenyl or aryl group. Furthermore, starting from a single mirror image form of the secondary alcohol, either mirror image form of the tertiary alcohol can be made with high levels of stereocontrol. Thus, a broad range of tertiary alcohols can now be easily made by this method with very high levels of selectivity. We expect that this methodology could find widespread application, as the intermediate tertiary boronic esters can potentially be converted into a range of functional groups with retention of configuration.

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[Chemical reaction: See text] The neuropeptide oxytocin 1 controls mammary and uterine smooth muscle contraction. Atosiban 2, an oxytocin antagonist, is used for prevention of preterm labor and premature birth. However, the metabolic lifetimes of such peptide drugs are short because of in vivo degradation. Facile production of oxytocin analogues with varying ring sizes wherein sulfur is replaced by carbon (methylene or methine) could be achieved by standard solid-phase peptide synthesis using olefin-bearing amino acids followed by on-resin ring-closing metathesis (RCM). These were tested for agonistic and antagonistic uteronic activity using myometrial strips taken from nonpregnant female rats. Peptide 8 showed agonistic activity in vitro (EC50= 1.4 x 10(3) +/- 4.4 x 10(2) nM) as compared to 1 (EC50= 7.0 +/- 2.1 nM). Atosiban analogues 17 (pA2= 7.8 +/- 0.1) and 18 (pA2= 8.0 +/- 0.1) showed substantial activity compared to the parent oxytocin antagonist 2 (pA2= 9.9 +/- 0.3). Carba analogue 35 (pA2= 6.1 +/- 0.1) had an agonistic activity over 2 orders of magnitude less than its parent 3 (8.8 +/- 0.5). A comparison of biological stabilities of 1,6-carba analogues of both an agonist 8 and antagonist 18 versus parent peptides 1 and 2 was conducted. The half-lives of peptides 8 and 18 in rat placental tissue were shown (Table 2) to be greatly improved versus their parents oxytocin 1 and atosiban 2, respectively. These results suggest that peptides 8 and 18 and analogues thereof may be important leads into the development of a long-lasting, commercially available therapeutic for initiation of parturition and treatment of preterm labor.

Facile synthesis of cis and trans olefinic analogues of oxytocin 1 that have carbon in place of sulfur is achieved via ring-closing metathesis (RCM) on a resin-bound linear precursor peptide. Hydrogenation of the cis olefin, 3, proceeds selectively to generate the previously reported saturated derivative 5. Biological testing on rat uterus strips shows that cis compound 3 has an EC50 value of 38 ng/mL (EC50 for oxytocin is 2.7 ng/mL) whereas 5 and trans olefin 4 are less active. [reaction--see text]

The type IIa bacteriocins are antimicrobial peptides isolated from lactic acid bacteria that act as food preservation agents and have nanomolar activity against pathogens such as Listeria monocytogenes. Previous reports with mutant bacteriocins indicate that the conserved disulfide bridge between cysteine residues 9 and 14 in bacteriocins such as leucocin A (1) is critical for antibiotic properties, which are mediated by target membrane receptor proteins belonging to the mannose phosphotransferase (mpt) system. To examine whether the disulfide can be replaced by an olefin moiety, [9,14]-dicarba leucocin A (4) was made by on-resin ring closing metathesis of allyl glycine residues using a new protocol suitable for larger hydrophobic peptides. Carbocyclic analogue 4 still displays nanomolar activity but is about 10-fold less potent than 1. Surprisingly, the acyclic [9,14]-diallyl leucocin A (5) displays even higher antibiotic activity than 4 and is as effective as the parent, leucocin A (1). We attribute this activity to hydrophobic intermolecular interactions of the diallyl side chains of the acyclic bacteriocin 5 that assist realization of the correct conformation at the receptor active site. Such substitutions in other systems may allow linear acyclic peptides to mimic the biological activity of natural disulfide ring-containing parents.