LONDON/NEW YORK (Reuters) – Alan Schwartz knows how to play a long game. The executive chairman of boutique investment bank Guggenheim Partners spent almost 20 years cultivating Pfizer boss Ian Read as a client. His strategy paid off handsomely when Guggenheim was named lead adviser for one of the biggest deals in history – Viagra-maker Pfizer’s $160 billion acquisition of Botox-maker Allergan .