We report the solid phase synthesis and some pharmacological properties of seven position two analogues (peptides 1–7) of one of our lead oxytocin antagonists. des‐9‐glycinamide[1‐(β‐mercapto‐β, β‐pentamethylenepropionic acid), 2‐O‐methyltyrosine, 4‐threonine]ornithinevasotocin(desGly‐NH2,d(CH2)5‐ [Tyr(Me)2,Thr4]OVT) (A). Peptides 1–7 have the following substituents at position two (1) d‐Tyr(Me); (2) l‐Tyr(Et); (3) d‐Tyr(Et); (4) l‐Tyr; (5) d‐Tyr; (6) d‐Phe and (7) d‐Trp. These were evaluated for agonistic and antagonistic activities in in vitro and in vitro OT assays, in vivo vasopressor (V1a‐receptor) assays and in vivo antidiuretic (V2‐receptor) assays. None of the seven peptides exhibits oxytocic or vasopressor agonism. Peptides 1,2,4,6 and 7 are extremely weak V2 agonists (V2 activities range from 0.001 to 0.02 U/mg). Peptides 3 and 5 exhibit weak V2 antagonism (pA2>6.0 and >5.5, respectively). Peptides 1–7 exhibit potent in vitro (no Mg2+) OT antagonism (anti‐OT pA2 values range from 7.66 to 8.03). Peptides 1 and 4–7 exhibit potent in vivo OT antagonism. Estimated in vivo anti‐OT pA2 values range from 7.06 to 7.79 (peptides 2 and 3 were not tested). With anti‐Vla pA2 values of 5.17‐6.25 all seven peptides exhibit reduced anti‐V1a, potencies relative to the parent peptide (A) (anti‐V1a. pA2= 6.46). Four of these peptides (4‐7) exhibit striking gains in in vitro and in vivo anti‐OT/anti‐V1a. selectivities compared to (A) which has an in vitro selectivity of 30 and an in vivo selectivity of 18. The d‐Tyr2 (5), d‐Trp2 (7), d‐Phe2 (6) and l‐Tyr2 (4) analogues of (A) exhibit anti‐OT (in vitro)/anti‐V1a selectivities = 240, 390, 404 and 540, respectively. The l‐Tyr2 (4), d‐Trp2 (7), d‐Phe2 (6)and d‐Tyr2 (5) analogues exhibited anti‐OT (in vivo)/anti‐V1a selectivities of 72, 80, 88 and 95, respectively. Peptides 4–7 appear to be the most selective peptide OT antagonists reported to date. In this regard it may be noted that they appear to be as or more potent and much more selective than the closely related OT antagonist 1‐deamino[D‐Tyr(Et)2,Thr1]OVT (Atosiban) which is currently undergoing clinical trial as a potential therapeutic agent for the prevention of premature labor. Atosiban (peptide 8) was resynthesized and pharmacologically evaluated in our laboratories. Atosiban exhibits the following antagonistic potencies. Anti‐OT (in vitro, no Mg2) pA2= 7.71; anti‐OT in vivo pA2= 7.05; anti‐V1 pA2= 6.14 and anti‐V2 pA2≅ 5.9. Its anti‐OT (in vivo)/anti‐V1a selectivity is 8. Some of these antagonists may be suitable candidates for evaluation as potential tocolytic agents for use in the treatment of pre‐term labor. They could also serve as useful new pharmacological tools for studies on the physiological roles of oxytocin. Finally, the findings presented here provide useful clues for the design of more potent and more selective OT antagonists.

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SummaryThe combined antiviral effect of dextran sulphate (OS, MW 40000) and acyclovir (ACV) on herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) in vitro and on experimental HSV-1 keratitis in rabbits, was studied, Dextran sulphate ilJ' combination with ACV results in synergistic effect,.a,'$ measured by yield ';'.' .~r eduction assay and on herpes",simplex keratitis in rabbits. The better therapeutic effect of the combination was proved by the decreased severity 'of ocular infection and the reduction of the virus shedding in tear film.