You could try many of the sprays on the market for deterent. But frankly leather and cats do not generally mix. Leather is smoother then fabric so even if the cat is not actively scratching the furniture by using it as a scratching post, the claws will come out for traction.
Against all popular belief cats sometimes miss when they jump on top of furniture, again out come the claws as they clamber up the sides. Full out chasing games also tend to bring out the claws as they race about and try not to slip.
My suggestion, get furniture covers if you don't like the look, throw afghans over them, or resign yourself to the fact that cats are not interested in how good leather looks as they rush through your house on the way to another adventure.
Another good option is get claw covers or tips on the cats and trim nails consistantly.
i have put rugs on both ends of my couches, and now he won,t scratch the couch with the rugs on.....i put the couch pillows on end, he use to pee on the couch in one spot, and not he does not do that anymore,,but i cannot sit on the couch until i put the pillows down
as for my chair,,,,,,he does not see to scratch as much with age, thought he still does it now and then...i sort of gave up on my furniture, and i have decided if i have a cat ,,,,furniture damage will happen,,,just live with it and do the best you can.....cats claw because its in their nature to do it.