re = /(?<=[.])(?=[^\s])/m
str = 'The two platinum derivatives have been previously combined as they are not totally cross-resistant and as they share no overlapping toxicities.Patients with AOC, after the initial cytoreductive surgery were randomized to either 6 courses of paclitaxel at 175 mg/m2 as 3 h infusion plus Carboplatin at 7 AUC (Arm A) or Paclitaxel at the same dose plus Carboplatin again at 7 AUC for cycles 1,3,5, while for cycles 2,4,6 Cisplatin at 75 mg/m2 substituted for Carboplatin (Arm B).247 patients are analyzed.'
subst = ' '
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html