If I understand correctly, something like this loop for constructing formulae by permuting a list of variables into a response variable and predictor equations might be helpful to you:

all_variables <- c("x1", "x2", "x3", "x4", "x5")
for (i in 1:length(all_variables)){
  combo <- all_variables[-i]
  formula <- as.formula(paste(all_variables[i], "~", paste(combo, collapse = " + ")))
  #
  # use "formula" here
  # e.g.
  # print(formula)
  #
}

Hope this helps. Best regards,