The pentapeptide, thymopentin (Arg1-Lys2-Asp3-Val4-Tyr5) is known for its activity as an immunomodulating drug, but with limited half-life in plasma. In this first paper of a series of three studies, the synthesis of analogs stabilized at the peptide bond between the C-terminal amino acids via insertion of a ketomethylene moiety is described. N-Blocked pseudopeptides containing Val(k)Phe, Ala(k)Phe, and Val(k)Val units were prepared and attached to chloromethyl Merrifield resin via the carboxy terminal. Removal of the N-BOC group by trifluoroacetic acid was followed by sequential coupling with N-BOC dipeptides of aspartic acid to yield resin-bound N-BOC pseudotetrapeptides. Removal of N-BOC and coupling with N-BOC-r-N-tosylarginine followed by total cleavage of blocking groups and resin by HF afforded the target pseudopentapeptides. The analogs were found to compete favorably with thymopentin for binding to CEM cells, but binding was reduced by about 20-30% on average. All analogs showed significant enhancement of half-life versus thymopentin in mouse serum, but most showed only modest improvement in human serum. Insertion of proline or norleucine at position 2 in the chain caused a substantial increase in half-life (3-4-fold), while N-methylnorleucine conferred complete stability in the analogs.
The binding of folate to Lactobacillus casei dihydrofolate reductase in the presence and absence of NADP+ has been studied by 15N NMR, using [5-15N]folate. In the presence of NADP+, three separate signals were observed for the single 15N atom, in agreement with our earlier evidence from 1H and 13C NMR for multiple conformations of this complex [(1982) Biochemistry 21, 5831-5838]. The 15N spectra of the binary enzyme-folate complex provide evidence for the first time that this complex also exists in at least two conformational states. This is confirmed by the observation of two separate resonances for the 7-proton of bound folate, located by two-dimensional exchange spectroscopy.
Several derivatives of the potent angiotensin converting enzyme inhibitor 5(S)-benzamido-4-oxo-6-phenylhexanoyl-L-proline (1) were synthesized and tested for converting enzyme inhibition activity and blood pressure lowering effects in rats. One compound, 5(S)-benzamido-2(R)-methyl-4-oxo-6-phenylhexanoyl-L-proline (2a), had and I50 against angiotensin converting enzyme of 1.0 x 10(-9) M and is the most potent inhibitor prepared thus far in this class of compounds. Testing of 2a orally at 30 mg/kg for inhibition of the angiotensin I induced blood pressure increase in conscious normotensive rats gave 100% inhibition that required 143 min before the angiotensin I blood pressure response returned to 70% of the pretreatment control response. In the conscious renal hypertensive rat, 2a given orally at a dose of 3 mg/kg caused a lowering of blood pressure that reached its maximum of 40 mmHg 8 h following drug administration.
Two simplified analogs of the dimeric naphthalenyltetrahydroisoquinoline alkaloid michellamine B [4′,4″‐didesmethoxy‐2′,2″‐didesmethylmichellamine B and 6,8‐dihydroxy‐5‐(1′,1″‐dihydroxy‐2′,2″‐binaphthalen‐4′‐yl)‐1R,3R‐dimethyl‐1,2,3,4‐tetrahydroisoquinoline] were synthesized using Suzuki palladiumcatalyzed biaryl cross‐coupling of 4‐(2‐benzyl‐6,8‐dibenzyloxy‐1R,3R‐dimethyl‐1,2,3,4‐tetrahydroisoquinolin‐5‐yl)‐1‐benzyloxy‐2‐bromonaphthalene to its corresponding atropisomeric 2‐naphthaleneboronic acid and 1‐benzyloxy‐2‐naphthaleneboronic acid, respectively. These analogs inhibited recombinant HIV reverse transcriptase with IC5() values of 62 μM and 1000 μM, respectively, whereas the IC5() value for michellamine B was 33 μM. Both michellamine B and the analogs inhibited the phosphorylation of histories by rat brain protein kinase C. The analogs were more active (IC50 values of 36 μM and 30 μM, respectively) than michellamine B (IC50 = 130 μM).
Carbonation of the dianions (LDA) of 5-methylthiophene-2-carboxylic, 2-methylpyridine-5-carboxylic, and 3-methylpyridine-6-carboxylic acids provided the respective carboxy heteroarylacetic acids. The crude diacids were directly esterified in MeOH-HCl to afford the diesters. Alkylation of the sodio anions with ethyl iodide yielded the appropriate alpha-ethyl diesters. The anions of the various diester substrates were then alkylated by 2,4-diamino-6-(bromomethyl)-pteridine followed by ester saponification at room temperature to afford the respective 2,4-diamino-4-deoxy-10-carboxy-10-deazapteroic acids. The 10-carboxyl group was readily decarboxylated by heating in DMSO at temperatures of 110-135 degrees C to give the diamino 10-deaza heteropteroic acid intermediates. Coupling with diethyl L-glutamate followed by ester hydrolysis afforded the target aminopterins. The analogues were evaluated for antiinflammatory effect in the mouse type II collagen model. The thiophene analogue of 10-ethyl-10-deazaaminopterin was found to be an effective inhibitor in terms of reduced visual evidence of inflammation and swelling as determined by caliper measurement.
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