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As part of a program aimed at designing more potent and selective antagonists of the antidiuretic responses to arginine-vasopressin (AVP), the authors substituted O-alkyl-D-tyrosine (where alkyl=methyl, ethyl, isopropyl, or n-propyl) at position 2 in our eight previously reported O-alkyl-L-tyrosine antagonists of antidiuretic and vasopressor responses to AVP. The authors also substituted D-tyrosine for L-tyrosine in two vasopressor antagonists with weak antidiuretic agonistic activity, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),4-valine,8-D-arginine]vasopressin [d(CH2)5VDAVP] and its L-arginine isomer [d(CH2)5VAVP]. The ten analogues, synthesized by the solid-phase method, are as follows: 1) d(CH2)5-D-Tyr(Me)VDAVP; 2) d(CH2)5-D-Tyr(Et)VDAVP; 3) d(CH2)5-D-Tyr(i-Pr)VDAVP; 4) d(CH2)5-D-Tyr(n-Pr)VDAVP; 5) d(CH2)5-D-Tyr(Me)VAVP; 6) d(CH2)5-D-Tyr(Et)VAVP; 7) d(CH2)5-D-Tyr(n-Pr)VAVP; 8) d(CH2)5-D-Tyr(i-Pr)VAVP; 9) d(CH2)5-D-TyrVDAVP; 10) d(CH2)5-D-TyrVAVP. These analogues were tested for agonistic and antagonistic activities in rat antidiuretic and rat vasopressor systems. All ten D-tyrosine analogues possess transient weak antidiuretic activities (0.004-0.05 U/mg). Subsequent doses of AVP are reversibly antagonized for 1-3 h, depending on the dose of the antagonist. They exhibit the following antidiuretic pA2 values: 1) 7.19±0.11; 2) 7.59±0.04; 3) 7.51±0.06; 4) 7.60±0.05; 5) 7.77±0.07; 6) 7.81±0.07; 7) 7.66±0.11; 8) 7.61±0.06; 9) 7.03±0.05; 10) 7.51±0.08. They are all effective antagonists of vasopressor responses to AVP. Analogues 1-8 are two to ten times more potent than their respective O-alkyl-L-tyrosine isomers as antidiuretic antagonists. Since the vasopressor potencies of the O-alkyl-L-tyrosine analogues have either diminished or remained virtually unchanged, these analogues exhibit a selective increase in their antiantidiuretic/antivasopressor ratios with respect to their respective O-alkyl-L-tyrosine analogues. The finding that the substitution of an unalkylated D-tyrosine for L-tyrosine in d(CH2)5VDAVP and d(CH2)5VAVP converts these weak antidiuretic agonists into potent antagonists of antidiuretic responses to AVP is highly significant, especially in view of the relative ease of synthesis and much higher yields of unalkylated vs. alkylated tyrosine analogues. These ten new analogues are potentially useful as pharmacological tools and as therapeutic agents. The findings presented here have also obvious potential for the design of even more potent and selective antidiuretic antagonists.
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Chiral nitrogen ligands in late transition metal-catalysed asymmetric synthesis—I. Addressing the problem of ligand lability in rhodium-catalysed hydrosilations,
Nitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous Catalysis