Peptides containing dipropylglycine. Part 1. Preparation of protected derivatives of dipropylglycine and their incorporation into dipeptides.

Methods for the incorporation of the hindered amino acid 2-amino-2-propylpentanoic acid (dipropylglycine, Dpg) into peptides have been investigated. Limitations on the preparation of protected derivatives of Dpg are discussed, and common methods of coupling examined. These methods are not subject to problems when used to link protein amino acids to the amino group of Dpg, but steric hindrance severely limits efficient peptide bond formation by the carboxyl group of Dpg. Only two reagents proved useful in this respect. N-Benzyloxycarbonyl (Z) Dpg can be coupled through its derivative with 3-hydroxy-4-oxo-3,4-dihydrobenzotriazine; other methods of activation of Z-Dpg tend to lead to formation of 2-benzyloxy-4,4-dipropyloxazolin-5(4H)-one, which resists attack by nucleophiles. 2-Trifluoromethyl-4,4-dipropyloxazolin-5(4H)-one, however, which is readily prepared from N-trifluoroacetyl-Dpg and thionyl chloride, couples cleanly with other amino acids, making it the reagent of choice for introduction of a Dpg residue.

Peptides containing dipropylglycine. Part 2. Preparation of tripeptides and higher homo-oligomers of dipropylglycine.

Using 4-heptanone in the Ugi reaction, it is possible to prepare a peptide containing a single residue of dipropylglycine (Dpg) in modest yield, but attempts to form peptides containing contiguous Dpg residues were unsuccessful. Methods of extending Dpg-Dpg to higher homo-oligomers have been examined. Carboxyl extension of N-trifluoroacetyl (Tfa)-Dpg2 is possible through its oxazolin-5(4H)-one, but only as far as the tripeptide. However, amino extension of Dpg2-OBut by successive steps of addition of 2-trifluoromethyl-4,4-dipropyloxazolin-5 (4H)-one and N-deprotection allowed preparation of Tfa-Dpg6-OBut in good yield. Removal of the Tfa group from Dpg residues is only possible using sodium borohydride reduction under conditions which lead to partial reduction of the t-butyl esters of protein amino acids. The use of the N',N'-dibenzylhydrazide (DBH) group for C-protection, however, circumvents this problem. Direct regeneration of carboxyl from DBH is possible with bromine in acetonitrile, and catalytic reduction gives the free hydrazide. Tfa-Dpg--NHNH2 can be oxidatively coupled to Gly-OBut but not to Dpg-OBut. Tfa-Dpg3-N3 undergoes Curtius rearrangement in preference to peptide bond formation, and Dpg3-N3 eliminates isocyanic acid on heating to form N-(Dpg)2-heptylideneimine.

Structure-activity relationships for the lipid-mobilising action of locust adipokinetic hormone. Synthesis and activity of a series of hormone analogues.

A series of compounds structurally related to adipokinetic hormone, the decapeptide neurohormone less than Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH2, have been prepared by synthesis and by enzymic cleavages of synthetic hormone. Their relative agonist activities in mobilising lipids over a fixed time interval (1 h) in locusts were assessed. The similar time courses for lipid release shown by two of the peptide analogues and adipokinetic hormone suggest that the analogues and the hormone are transported to the receptors on the fat body cells, and are also degraded, at similar rates. Consequently, the analogue activities can be correlated with the structural requirements of the locust fat body hormone receptors. The requirements for activity demonstrated in this study are as follows. Residues 1--8 from the N-terminus are necessary to elicit some activity (20%). Residues 5 and 7 in the octapeptide can be changed without affecting activity but L-pyroglutamic acid as the N-terminal residue is necessary formaximum activity both in the octapeptide and the decapeptide. Full activity is achieved only by adding the dipeptide glycyl threonine amide to the active octapeptide 'core'. In the decapeptide, residues cannot be interchanged to the same extent as in the octapeptide without reducing activity. The peptide probably has to be uncharged. Inactive analogues of seven residues or less do not interfere in the hormone-receptor interaction.

Reagents for the preparation of two oligonucleotides per synthesis (TOPS).

In order to increase the efficiency of use of automated DNA synthesizers (i.e. the number of oligomers prepared per day), we have devised and prepared novel phosphoramidite reagents that contain a linking group which, while stable under the normal synthesis conditions, is cleaved under basic conditions. When one of these linkers is introduced at the desired position in the synthesis of an oligonucleotide, subsequent detritylation enables the synthesis of a second oligonucleotides sequence upon the first. During deprotection of the oligonucleotide with ammonium hydroxide, the chain is cleaved at either side of the points of introduction of the novel reagent, generating two oligonucleotides free in solution. These reagents are of particular use in applications where oligomers are used in pairs (such as PCR, chemical synthesis of genes etc.) and means that an automated synthesis facility can be used more efficiently, without the need for operator intervention, after the working day is over.

Prognostic value of the stress response following stroke.

The systemic metabolic response following intracranial vascular damage was measured in 65 consecutively seen patients (56 with cerebral infarction and nine with subarachnoid hemorrhage). Significantly (P less than .01) greater mortality and eventual disability occurred in patients excreting more than 200 microgram of urinary norepinephrine and epinephrine daily early in their acute illness. These patients also had significantly (P less than .001) elevated plasma cortisol levels; this measurement may prove useful in predicting prognosis after stroke. Cardiac abnormalities resulting from the elevated catecholamine levels may contribute to the excess mortality in those patients with an intense stress response.

Preferred conformation of peptides from C alpha,alpha- symmetrically disubstituted glycines: aromatic residues.

The conformational preference of C(alpha,alpha-diphenylglycine (D-phi-g) and C(alpha,alpha)-dibenzylglycine (Dbz) residues was assessed in selected derivatives and small peptides by conformational energy computations, ir absorption, 1H-nmr, and x-ray diffraction. Conformational energy computations on the two monopeptides strongly support the view that these C(alpha,alpha)-symmetrically disubstituted glycines are conformationally restricted and that their minimum energy conformation falls in the fully extended (C5) region. The results of the theoretical analyses appear to be in agreement with the solution and crystal-state structural propensities of three derivatives and seven di- and tripeptides.