Two friends raised more than £3,000 from their run in memory of a keen adventurer who died in a paragliding accident in the Spanish Pyrenees at the age of 25.
Ben Jacobs, 25, and Simon Azouelos, 24, were already planning to run the marathon when they discovered that the family of their schoolfriend Guy Joseph was setting up a foundation in his name.
Mr Joseph had worked as a professional scuba-diving instructor in East Timor and the memorial foundation will help impoverished families and alleviate illiteracy in the Kaski district of Nepal, where he spent several months before he died.
Half the money will go to the Gauchers Association, supporting those with the disease, for which one-in-12 Ashkenazi Jews is a carrier.
Mr Jacobs has a cousin with Gauchers and is involved in the association.
The genetic condition results in malfunctioning spleen and liver, anaemia, bruising, tendency to bleed, bone pain, degeneration of kidneys and lung problems.
Gauchers can be treated but at a cost of up to £130,000 annually per patient.
Mr Jacobs, a media buyer from north London, reached the finish in four hours 26 minutes. Mr Azouelos took just over six hours. Mr Jacobs said the Joseph family had appreciated their efforts.
"They were mainly surprised that two of Guy's laziest friends planned to run the London Marathon," he explained.